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UNIVERSITY OF HAW,L\I'I LlE'RARY

LOW-COST MICROSTRIP LINE-BASED FERRITE PHASE SHIFfER

A THESIS SUBMI'l"I'ED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAW AI'I IN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

IN

ELECTRICAL ENGINEERING

AUGUST 2006

By William W.G. Rui

Thesis Committee:

Magdy F. Iskander, Chairperson M. Fatih Demirkol

Zhengqing Ynn

We certify that we have read this thesis and that, in our opinion, it is satisfactory in scope

and quality as a thesis for the degree of Master of Science in Electrical Engineering.

AWN Qlll .H3

no. 4085

ii

ACKNOWLEDGMENTS

I would like to thank my friends and family for all their support and love. I would like to

thank my two older sisters, Kimberly and Irene, for helping me out and watching over me

all these years. Also I would like to thank my parents, Anna and Kwok Chau Hui, for

raising me and sacrificing everything they had to come to America. They are the reason

for my success and my reason for always trying to achieve my goals so one day I could

repay them back for all the hard work they have done for our family. I would like to

thank my colleagues at the Hawai'i Center for Advanced Communications (HCAC),

Jodie Bell, Nuri Celik, Wayne Kim, and Chad Takahashi for all their help and inputs in

helping with my project. I would like to especially thank Mr. Jodie Bell for helping me

out in my research project and helping me use Ansoft HFSS for my simulation results. I

would like to thank my committee members Dr. Zhengqing Yun and Dr. M. Fatih

Demirkol for all their inputs and for their valuable feedbacks. and guidance. Also I would

like to thank Mr. Ben Respicio. Mr. Brian Kodama, and the rest of the staff at the

engineering shop in the University ofHawai'i at MlInoa, College of Engineering, for

fabricating the prototype. Lastly I would like to give my thanks to my advisor, Dr.

Magdy F. Iskander, for giving me a chance to be part ofhis research team and giving me

an opportunity to work in this challenge and innovating field. Also I would like to thank

him for having the vision in making this research project, a successful one and for

coming up with new ideas in improving the project.

iii

ABSTRACf

High-gain, electronically-scanned phased array antennas are commonly used for radar

and communications applications. These systems often require thousands of radiating

elements, which in turn require thousands of phase shifters. Therefore, reduction in cost,

size, and weight is important goal to provide an optimized overall system.

This thesis presents a new ferrite phase shifter design based on microstrip line technology

that provides reduction in cost, size, and weight as compared to typical ferrite (analog)

phase shifters. The design is based on the use of three microstrip lines arranged and fed

with phase differences so as to produce circular polarization in the ferrite region. The

proposed ferrite phase shifter was designed and simulated at 3 GHz to achieve a phase

shift of approximately 3600 in less than an effective wavelength. Two prototypes were

designed and fabricated to provide optimal circular polarization in the ferrite region and

measured results shows, that the second prototype phase shifter achieved 3090 of phase

shift in a wavelength, thus fidfilling the requirements. Additional studies on the bias coil

provided an external to internal H-field ratio, should be applied to the experimental bias,

which leads to better agreement between simulation and experimental results than

otherwise. Based on the successful development of previous prototypes, suggestions are

made for further improvements including reducing the number of turns in the biasing coil

and minimize the required input power.

iv

TABLE OF CONTENTS

Acknowledgments ................................................................... iii Abstract ....................................................................................................................................................... iv List of Tables ........................................................................................................ , ............. vi L· fF' .. 1St 0 19ures ............................................................................................... VII

Chapter I: Introduction ............................................................. I Chapter 2: Previous Designs ........................................................ 8 Chapter 3: Design and Simulation of Microstrip Line-Based Ferrite Phase Shifter- 3 mm .............................................................................................. 16

Simulation Results .......................................................... 21 Chapter 4: Fabrication of Micros trip Line-Based Ferrite Phase Shifter -3 tnm ................................................................................................................. 26

Bias Coil and Experimental Results ...................................... .31 Chapter 5: Design and Simulation of Microstrip Line-Based Ferrite Phase Shifter - 5 mm ............................................................................................. 40

Simulation results ............................................................ 43 Chapter 6: Fabrication of Micros trip Line-Based Ferrite Phase Shifter -5 mm ............................................................................................................. 47 Chapter 7: Experimental Results of Microstrip Line-Based Ferrite Phase Shifter - 5 rnm ............................................................................................... 54 Chapter 8: Conclusion and Future Works ........................................ 68 References ................................................................................................... 73

v

LIST OF TABLES

1.1 Comparison of the advantage and disadvantage of the four main types ofRF phase shifters ............................................................ 6

3.1 Comparison between 0 - 30 kAlm for insertion loss and return loss of the ferrite loaded waveguide at 3GHz .........................•. .17

3.2 Comparison table between 600 Gauss and 1750 Gauss ferrite at 3GHz ....... 18

3.3 Results of the proposed microstrip line-based ferrite phase shifter design of return loss and insertion loss at no bias (0 kAlm) ..........•................. 22

3.4 Results of the proposed microstrip line-based ferrite phase shifter design of return loss, insertion loss, and total phase shift (norma1ized to wavelength) at no bias (0 kAlm) and at full bias (200 kAlm) .................. 24

5.1 Table of the new microstrip line-based ferrite phase shifter (5 mm) insertion loss, return loss, and insertion phase at 0 and at full (200 kAlm) bias .................................................................. 46

vi

LIST OF FIGURES

Figure l!wl

1.1 Reggia-Spencer reciprocal phase shifter ............................................................ 2

1.2 Nonreciprocal Faraday-rotation phase shifter ................................................... .3

1.3 Geometry of twin-toroid ferrite phase shifter .................................................... 4

1.4 Dual-mode ferrite phase shifter ......................................................................... 5

2.1 Cross-sectional view of a planar microstrip line ferrite phase shifter ............... 8

2.2 Top view of a planar microstrip line ferrite phase shifter ........................•........ 9

2.3 Geometry of the transmission -line phase shifter section of the ferrite phase shifter ........................................................................................... 11

2.4 Cross section of the previous non-planar ferrite phase shifter using Ansoft HFSS; verify circular polarization ............................................. 12

2.5 The feed-network design for the non-planar microstrip line ferrite phase shifter, utilizes a quarter-wave transformer ........................................... 12

2.6 The complete previous non-planar microstrip line ferrite phase shifter with a rectangnlar ferrite slab ..•....................................................................... 13

2.7 Insertion loss (Sd vs. internal magnetic bias .................................................. 14

2.8 Phase shift (S12 insertion phase) vs. internal magnetic bias ............................. 15

2.9 The fabricated previous 3 GHz non-planar microstrip line ferrite phase shifter .......................................................................................... 15

3.1 Diagonally view of a ferrite loaded waveguide ............................................... 16

3.2 Diagonally view of the proposed microstrip line-based ferrite phase shifter .......................................................................................... 18

3.3 Top view of the proposed microstrip line-based ferrite phase shifter ..................................................................................................... 20

vii

3.4 Cross section view of the proposed microstrip line-based fenite phase shifter .......................................................................................... 21

3.5 Cross section view of the proposed microstrip line-based fenite phase shifter. Observing the simulation it verifies circular polarizations in the fenite slab region ............................................... 21

3.6 Graph of Insertion loss (S21) vs. internal magnetic bias of the new proposed microstrip line-based fenite phase shifter at 3 GHz .................•.................... 23

3.7 Graph ofRetum loss (SII) vs. internal magnetic bias of the new proposed microstrip line-based fenite phase shifter at 3 GHz ...................................... 24

3.8 Graph of Insertion phase (S21) vs. internal magnetic bias of the new proposed microstrip line-based fenite phase shifter at 3 GHz .......................•.............. 25

4.1 Substrate nsing Roger Corporation TMM lOi material .........................•....... .26

4.2 Materials for the newly proposed microstrip line-based fenite phase shifter: fenite slab, substrate, and non-planar structure ............................................... 27

4.3 New non planar structure ....................................................•.....•....•................. 28

4.4 The feed network after photo-laminate process ............................................... 29

4.5 Complete prototype of micro strip line-based fenite phase shifter, hand cut version of the feed network ......................................... 30

4.6 Complete prototype of microstrip line-based fenite phase shifter, photo-laminate version of the feed network .............................. 30

4.7 Cross section of microstrip line-base fenite phase shifter ........................ 32

4.8 The bias coil after more layers of magnetic wire were added ....................•.... 31

4.9 Screen shot of retum loss, insertion loss and insertion phase at no bias .•.....•. 32

4.10 Screen shot of retum loss, insertion loss and insertion phase at 2.65A ..............................................................................................•............. 33

4.11 Screen shot of retum loss, insertion loss and insertion phase with a new DC power supply at 0 bias ............................................................. 34

viii

4.12 Screen shot of the return loss, insertion loss and insertion phase with a new DC power supply at lOA or full bias ............................................ .35

4.13 Top view of micro strip line-based ferrite phase shifter (3mm) when substrate is cut to fit the new bias coil around the ferrite region .................................... 36

4.14 Another view of micro strip line-based ferrite phase shifter (3mm) when substrate is cut to fit the new bias coil around the ferrite region ....•................ 36

4.15 Complete microstrip line-based ferrite phase shifter (3mm) with the new bias coiL .............................................................................................................. 37

4.16 Side view of the complete microstrip line-based ferrite phase shifter (3 mm) with the new bias coil ...................................................................................... 38

4.17 Screen shot of the insertion loss, return loss, and insertion phase with the new bias coil when no bias is applied ................................................ 38

4.18 Screen shot of the insertion loss, return loss, and insertion phase with the new bias coil when full bias is applied .............................................. 39

5.1 Cross section of the new design of the microstrip line-based ferrite phase shifter (5 mm) with a larger ferrite slab cross section of3 x 5 mm ............................ 41

5.2 The feed network in Ansoft HFSS of the new microstrip line-based ferrite phase shifter (5 mm) with a larger ferrite slab 3 x 5 mm ...............••............... .41

5.3 The complete design of the new microstrip line-based ferrite phase shifter (5 mm) with a larger ferrite slab 3 x 5 mm ...................................................................... 42

5.4 The top view of the new micro strip line-based ferrite phase shifter (5mm) with a larger ferrite slab 3 x 5 mm ................................................................... 43

5.5 Graph of the Insertion loss S21 vs. internal magnetic bias at 3GHz ................. 44

5.6 Graph of the Return loss Sl1 vs. internal magnetic bias at 3GHz ................... .45

5.7 Graph of the insertion phase S21 vs. intema1 magnetic bias at 3GHz .............. 46

6.1 Dielectric substrate material from Rogers Corporation .................................. .47

6.2 The new non-planar structure for the larger ferrite slab of3 x 5 mm .............. 48

ix

6.3 The new ferrite slab material, nickel aluminum with 3 x 5 mm cross section ............................................................................. 49

6.4 The feed network after photo-laminate process and copper etch ....•.............. .49

6.5 The complete microstrip line-based ferrite phase shifter prototype (5 mm) without the bias coil ..............................•..............................................•........... 50

6.6 Another view of the complete microstrip line-based ferrite phase shifter prototype (5 mm) without the bias coil ............................................................ 51

6.7 Top view of the complete microstrip line-based ferrite phase shifter prototype (5 mm) without the bias coil ............................................................................ 51

6.8 cross section view of micro strip line-based ferrite phase shifter prototype (5mm) without the bias coiL ...................................................•............... 52

6.9 The complete microstrip line-based ferrite phase shifter prototype (5 mm) with the bias coil ..........................••.................................................................. 52

6.10 Another view of the complete microstrip line-based ferrite phase shifter prototype (5 mm) with the bias coil ................................................................ 53

6.11 Top view of the complete microstrip line-based ferrite phase shifter prototype (5 mm) with the bias coil.. .......................•....................................... 53

7.1 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) when no bias is applied .............................................................•....•................ .54

7.2 Screen shot of new micro strip line-based ferrite phase shifter prototype (5 mm) when full bias is applied .................................................................................. 55

7.3 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) before phase transition ......................................................•.............................. 56

7.4 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) after phase transition ........................................................................................ 56

7.5 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) when no bias is applied .................................................................................... 57

7.6 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) when 3600 is achieved ..................................................................................... 58

x

7.7 Experimental return loss (S 11) results of the microstrip line-based ferrite phase shifter (5 mm) vs. internal magnetic bias ................................•........................... 59

7.8 Comparison between simulation return loss and experimental return loss results of the new microstrip line-based ferrite phase shifter (5 mm) ........................................................................................ 60

7.9 Experimental insertion loss (S21) results of the microstrip line-based ferrite phase shifter (5 mm) vs. internal magnetic bias .............................................. 60

7.10 Comparison between simulation insertion loss and experimental insertion loss results of the new microstrip line-based ferrite phase shifter (5 mm) .............................................................................................................. 61

7.11 Experimental insertion phase (S21) results of the microstrip line-based ferrite phase shifter (5 mm) vs. internal magnetic bias •............................................. 62

7.12 Comparison between simulation insertion phase and experimental insertion phase results of the new microstrip line-based ferrite phase shifter (5 mm) ... 63

7.13 Comparison between simulation return loss and insertion loss and experimental return loss and insertion loss results of the new microstrip line-based ferrite phase shifter (5 mm) ........................................................... 64

7.14 Simple bias coil design in Ansoft HFSS ..........................•.................. 65

7.15 Bias coil simulated in HFSS to obtain a simulated H-field .................•.... 65

7.16 Comparison between simulation return and insertion loss and experimental return and insertion loss when applying the external to internal H -field ratio to the experimental results ............................................................ 66

7.17 Comparison between simulation insertion phase and experimental insertion phase when applying the external to internal H-field ratio to the experimental results .................................................................................... 67

8.1 Comparison between ferrite cross section where ferrite cross section of 7 x 9 mm shows a vast improvement of phase shift ........................................ 70

8.2 Future microstrip line ferrite phase shifter, where ferrite slab material's cross section is increase to 7 x 9 mm ................................................. 71

8.3 Cross section view of future microstrip line ferrite phase shifter, where ferrite material's cross section is increase to 7 x 9 mm .......................... 72

xi

8.4 S-parameters of future microstrip line ferrite phase shifter, where ferrite material's cross section is increase to 7 x 9 mm ................................... 72

xii

CHAPTER} INTRODUCTION

For high-gain antenna aITaYS, it comprised of thousand of radiating elements. Originally

the signal beams for these antenna aITaYS were steered mechanically, however due to

mechanical failures and time delay involved with mechanical rotation, the signal beams

are now electronically steered, which allows the antennas to remain stationary.

Electronically scanned aITaYS (ESAs) are phased aITay antennas that steer the signal beam

by changing the phase of the feed signal at each of the radiating aITay element; this is

done by placing a phase shifter before each mdiating element. A phase shifter is

essentially an electronic device that changes the insertion phase along a microwave signal

path without changing the actual physical path length.

Because a typical phased aITay antenna system consists of thousands of radiating

elements, therefore thousands of phase shifters are also needed. Therefore. low-cost,

compact phase shifters are required that can provide the full 360°analog range of phase

shift. Current ferrite phase shifters are waveguide-based technology and the phase shift is

maximizes over a given distance by producing circular polarized microwaves to interact

with the magnetic dipole moments in the biased ferrite material. Although this technique

produces the desired phase shift, it is costly to manufacture as the process involves

cutting to exact dimensions and positioning the ferrite rods inside the waveguide, and

also inserting the quarter-wave plates for impedance matching and achieving circularly

polarization. Therefore, the development of ferrite phase shifters utilizing low-cost

I

printed transmission lines technology would provide a low-cost alternative. Therefore

the goal of this thesis/research project is to design a low-cost, compact, lightweight,

microwave/millimeter-wave ferrite phase shifter that provides the full 3600 analog range

of phase shift to each antenna element.

There are four types of phase shifters - ferrite, PIN diode, MEMS, and ferroelectric.

There are three main types of ferrite phase shifters: twin toroid, dual-mode, and rotary

field [1]. Reggia and Spencer [2] successfully developed a reciprocal phase shifter,

which is basically an analog phase-shifting device, consisting of a longit1ldin ally

magnetized ferrite rod or bar placed at the center of a rectangular waveguide, shown in

Figure. 1.1. A solenoid coil surrounding the waveguide was used to bias the ferrite rod.

This device was able to produce a large phase shift over a relatively short distance.

Figure 1.2 shows a Faraday-rotation phase shifter, which is a nonreciprocal version of

Reggia-Spencer phase shifter [3].

Figure 1.1 Reggia-Spencer recipIucal phase shifter [3].

2

The Reggia-Spencer phase shifter is modified by placing a quarter-wave dielectric plate

at both ends of the axially biased ferrite rod. This converts a linearly polarized wave into

a circularly polarized wave, which interacts strongly or weakly with the biased ferrite

material depending on the sense of the polarization together with the direction of

propagation of the signal and the direction of the applied bias field The second quarter

wave plate transforms the circularly polarized wave back into a linearly polarized wave.

t

Figure 1.2 NomecipIiX:a1 Faraday-rotation phase shifter [3].

The twin-toroid ferrite phase shifter is a latching, nonreciprocal device that is comprised

of a dielectric spacer sandwiched between two ferrite toroids, enclosed in a metal

waveguide as shown in Figure. 1.3. The walls of the ferrite toroids that touch the

dielectric spacer are positioned so they lie in the regions of the waveguide which support

circularly polarized magnetic fields [1]. Having circularly polarized signal waves, as

opposed to linearly polarized waves, in the ferrite regions ensures a greater interaction

with the ferrite once it is biased, therefore providing more phase shift over a given

propagation distance than could otherwise be obtained The second common ferrite

3

phase shifter is the dual-mode design.

I I • t, ••

-I "4 fW] t"2 t2><, + "7t "31. "4 !-

c.,

fbI

Figure 1.3 Geometry of twin-toroid ferrite phase shifter [4]

Like the twin toroid, it is also a latching device; however. it exhibits reciprocal behavior

as opposed to nonreciprocal behavior. The dual-mode ferrite phase shifter is comprised

of a circular or quadranta1ly symmetric ferrite rod, and two nonreciprocal circular

polarizers at both ends of the ferrite rod as shown in Figure. 1.4. The ferrite rod is

metallized to form a ferrite-filled waveguide, and is sandwiched in the variable-field

section between external latching yokes (Figure 1.4), which provide the closed magnetic

path needed for latching-mode operation [3], [4]. The ferrite rod must have a

circular/quadrantal cross-section in order to ensure that circularly polarized microwave

signals will pass through it without having their field distribution distorted. The circular

polarizers convert linearly polarized waves to circularly polarized ones, and vice versa

4

Ralfiutor

"'!Chlng transforar

Sprlna c

I I_a!io; ....,..,.

I I I •

FIgure 1.4 Dual-mode ferrite phase shifter configuration showing the variable-field section and the nonreciptOOl! circu1ar polarizer [4].

The last of the three most common ferrite phase shifters is the rotary-field phase shifter,

which has traditionally been available in only a non-latching, reciprocal fonn. Within the

last decade, latching reciprocal rotary-field phase shifters have been developed [4],

allowing users to overcome the continuous-bias-current obstacle when implementing

these phase shifters into their microwave designs. The rotary-field phase shifter is

composed of a nonreciprocal rotatable ferrite half-wave plate situated in between two

fixed reciprocal quarter-wave plates. The ferrite half-wave plate is a composite

ferrite/dielectric rod, which has been metallized to fonn a circular waveguide. It is

surrounded by a drive yoke, which changes the angular orientation of the half-wave plate,

thus, providing a rotatable magnetic field with fixed amplitude. This rotatable magnetic

field is what provides the desired phase shift and with the added bonus of inherently low

phase error compared to the other two ferrite phase shifters. This is due to the fact that

the phase shift is controlled by adjusting the angular orientation of the bias field as

5

opposed to adjusting the magnitude of the bias field [3]. Each of the four main types of

RF phase shifter has certain advantages and disadvantages as shown in Table 1.1.

TIlles ofRF Phase Advantal!es Disadvantal!es

Shifters

Low-cost High loss Compact in size High power

PIN Diodes Intergrability wI planar consumption tech. Digital phase shift

Light in weight Moderate loss Low power Digital phase shift

MEMS consumption Not true high Compact in size frequency device Intergrability wI planar tech. Low power Expensive

Ferroelectric consumption High insertion loss Compact in size Analog phase shift Low loss Expensive Low power Heavy in weight

Ferrite consumption Moderate size Analog phase shift

Table 1.1 Companson of the advantages and disadvantages of the four mam types ofRF phase shifters.

Typical ferrite phase shifters provide the lowest RF loss [4]. Where as typical MEMS

phase shifter provide the smallest size and the lightest weight [5], however typical

MEMS phase shifter are not true high frequency devices, they do not operated in high

microwave frequency. Typical MEMS phase shifters are even lighter and smaller than

PIN diode phase shifters, but they add more RF loss (around 2 dB [6]) to the system than

typical ferrite phase shifters [5]. Typical ferrite phase shifters are heavy and expensive

due to the entail carefully positioning small-diameter ferrite rods inside metal waveguides

6

and as well as dielectric quarter-wave plates inside. Typical PIN diode phase shifters are

smaller, lighter, and cheaper than typical ferrite phase shifters; however, they experience

high loss 3 dB [5] and consume a great deal of power for proper operation [3]. Typical

ferroelectric phase shifters have analog phase shift due to dependent of a de electric field

and low power consumption, however are expensive due to the growth of the materials,

and very high insertion loss [7]. The remaining chapters in this thesis will focus on the

previous designs, new designs and simulations, and fabrication of the proposed ferrite

phase shifter including experimental results.

In Chapter 2, analysis of the planar microstrip line ferrite phase shifter proposed by Lee

and Strahan in their U.S. patent [8] as well as the previous design of the non-planar

microstrip line ferrite phase shifter[9], [10] will be described. Chapters 3 will focus on

the design, simulation, and analysis of the new purposed microstrip line-based ferrite

phase shifter. In Chapter 4 we will focus on fabrication of a new prototype microstrip

line-based ferrite phase shifter device and a new bias coil design. Another design of the

microstrip line-based ferrite phase shifter when the ferrite slab material is increase to 3 x

5 mm cross section will be explained in Chapter 5. Fabrication of the new microstrip

line-based ferrite phase shifter prototype (5 mm) will be discussed in Chapter 6. Testing

of the prototype will be described in Chapter 7, including comparisons between the

simulated S-parameter results and the measured data. Finally, Chapter 8 will offer future

work as well as a conclusion to this thesis by highlighting the key milestones of this

research project.

7

CHAPTER 2 PREVIOUS DESIGNS

In 1993, Lee and Strahan at Hughes Aircraft Company (currently Raytheon) proposed a

low-cost planar ferrite phase shifter that could theoretically produce circularly polarized

waves in the ferrite material as shown in Figure 2.1 and Figure 2.2. A U.S. patent [8)

was obtained for their invention. This particular microwave ferrite phase shifter consists

of three parallel micro strip lines on a ferrite substrate, which, is positioned on a ground

plane. A microstrip feed network was proposed at the input of the transmission lines to

provide a phase difference of 900 between the left and center microstrip lines. and -900

(270°) between the right and center microstrip lines.

Figure 2.1 Cross-sectional view of a planar microstrip line ferrite phase shifter consisting of a ferrite substrate sandwiched between three parallel microstrip 1ines and a ground plane [8].

8

A similar network was proposed at the output to reverse the phase offsets imposed at the

input and recombine the signals. By introducing these quadrature phase offsets at the

input, a vertical electric field was generated between the center microstrip line and the

ground plane, and a horizontal electric field between the left and right microstrip lines.

Lee and Strahan proposed that the superposition of these two electric fields would

produce a circularly polarized wave in the ferrite substrate.

91 r---------------------~ \1=~-'21

l1 FIgure 2.2 Top view of a planar microstrip line ferrite phase shifter consisting of a ferrite

substrate sandwiched between three pamllel microstrip lines and a ground plane [8].

The resultant circularly polarized signal, as it propagates toward the output terminal,

would encounter a strong interaction with the ferrite material. Due to this strong

interaction, the proposed phase shifter would achieve more phase shift per centimeter

than other ferrite phase shifters using printed-circuit technology; for example, achieve

3600 of phase shift in less than a few wavelengths [8].

Because of a Jack of suitable EM simulation tools, Lee and Strahan were not able to fully

analyze and optimize their novel phase shifter design. As part of a research contract in

9

2002, Lee and Strahan's ferrite phase shifter design was simuIated and analyzed at the

University ofHawai'i at M!noa using Ansoft's High Frequency Structure Simulator

(HFSS) software. No feed network was designed for this particular phase shifter;

instead, the three microstrip lines were each manually fed with a user-defined magnitude

and phase. Upon examining an animation of the electric-field vectors in the ferrite region

from taking a cross-sectional cut through the phase shifter, it was found that the

horizontal electric-field component described earlier was much weaker than the vertical

electric-field component, resulting in elliptical polarization rather than circular

polarization [9].

Therefore, to enhance the horizontal electric-field component in the ferrite material, the

planar ferrite phase shifter design was modified from a planar geometry to a non-planar

geometry. The center microstrip line of the transmission-line phase shifter section was

raised to a higher elevation, while the two outer microstrip lines were angled (45°)

inward to produce circularly polarized wave. Figure 2.2 shows a circular ferrite rod

embedded in the dielectric substrate, beneath the center microstrip line. The dielectric

constant of the ferrite slab and the dielectric substrate was selected at 11.3. The phase

shifter was designed to operate at 3 GHz (S-band). The planar section of the substrate

was chosen to be 3.2 rom thick. The center-offset portion of the non-planar structure was

extended an additional 2.5 rom above the planar section of the substrate.

10

Figure 2.3 Geometry of the transmission-line phase-shifter section of the ferrite phase shifter [9].

The ferrite slab material was chosen to have a magnetic saturation of 1750 Gauss, with a

cross sectional dimension of 1.3 mm x 6.3 mm with a length of 76 mm. The three

microstrip lines were chosen to be 3 mm; the center microstrip line runs parallel to the

ground plane, while the outer two microstrip lines are angled from the horizontal around

45°. Also Figure 2.4 shows the cross section of the non-planar phase shifter showing

circular polarization in the ferrite material region.

11

1._- - - ---- "- "-!:::= I / /' -. "~- \

I ----.. • \ -.i

/

• \ , \ \

Figure 2.4 Cross section of the previous non-planar ferrite pbase shifter, using Ansoft HFSS; verify that tbe ferri te slab region does produce a circular polarization [ 10].

A feed network was necessary to offset the phase and divide the input power between the

three rnicrostrip lines.

Figure 2.5 The feed-network design for the non-planar microstrip line ferrite pbase srufter. This design utilizes a quaner-wave transformer at the power-spliner junction [10].

12

A similar network was also needed at the ends of the microstrip lines to realign the phase

and recombine the power to produce one output signal. Figure 2.5 shows the feed

network design that was chosen, using a microstrip quarter-wave transformer at the

power splitter/combiner junction, reduces the reflection coefficient the input.

Figure 2.6 The complete non-planar microstrip line ferrite phase shifter with a rectangular ferrite slab embedded in the non-planar structure of the ceramic substrate [10].

Figure 2.6 shows the complete design of the previous non-planar ferrite phase shifter

with the feed network. Where using Ansoft HFSS, the complete structure was simulated

by running a parametric analysis that varied the magnitude of the internal magnetic bias

field in the ferrite form 0 to 160 kAlm. A plot of the insertion loss versus the magnetic

bias shown in Figure 2. 7, where in the low bias region the insertion loss is very high

around -20 dB.

13

0

-4

-III 'D

-8 -.. 'D a Ii. ·12 II :E

·18

·20 0 20

Ferrlte-slab Mlcrostrlp Phase Shifter

I • I • -

Ferrites are typically very lossy below saturation levels

40 80 80 100 120 140

Internal Magnetic Bias (kA/m)

180

FIgure Z.7 Insertion loss (StU vs. intemal magnetic bias. The high insertion loss for low bias values cmrespondiDg to the fact that feuites can be very lossy before they saturate [1 OJ.

Figure 2.8 the insertion phase versus the magnetic bias, where there is a 6720 of phase

shift, between no bias (0 kAlm) and full bias (160 kAlm). This equates approximately

3400 per wavelength which exceed Lee and Strahan's expectation of obtaining 3600 of

phase shift in just under a few wavelengths.

However, measuring the fabricated non-planar ferrite phase shifter prototype previously

designed shown in Figure 2.9, the phase shifter did not reach the desired operating bias

range of 40 to 160 kAlm. Even though a bigger bias coil was hand wound to produce

more magnetic field bias.

14

700

600

500

Ci 400 ~

l:. ~ 300 ~ .. .c 200 0..

100

a

-100 a

Ferrile-slab M icroslrip Phase Shifter

tlcp = 672°17 .62cm = SSo/em = 340°/)"

20 40 60 80 100 120 140

Internal Magnetic B ias (kA/m)

160

Figure 2.8 Phase shift (SI2 insertion phase) vs. internal magnetic bias [10].

The previous non-planar ferrite phase shifter prototype had a 26° increase in insertion

phase from 0 Wm to 0.56 Wm. The insufficient amount of insertion phase is probably

due to high insertion loss at the low bias region, which could be due to incorrect

impendence matching [10]. Solutions for the high insert.ion loss and insufficient phase

shift and as well as a new design are explained in more detail in Chapter 3.

Figure 2.9 The 3 GHz non-planar microstrip line ferrite phase shifter [10].

15

CHAPTER 3

D ESIGN AND SIMULATIO T OF MlCROSTRIP LINE-BASED FERRITE P HASE

SmFTER-3MM

As mention in Chapter 2 the previous design of the non-planar microstrip line ferrite

phase shifter, had certain problems with impedance matching. The previous design had a

high insertion loss at tbe low biasing region and this prevented measuring, so tbe change

in phase across a magnetic bias field with the increase in bias. One solution that

Raytheon suggested is to figure out if the ferrite material originally suggested is suitable

for the design frequency region at S-band. A study using a ferrite loaded waveguide

shown in Figure 3.1 was simulated using Ansoft 's HFSS to evaluate the performance of

the phase shifter when different ferrite materials are used.

Ferrite material

Dielectric material

Metal wave guide

j

Figure 3.1 Diagonally view of a ferrile loaded waveguide consisting of a dielectric slab sandwiched between two ferrite slabs. The waveguide is incased in a metal frame. where the ferrite loaded waveguide was simulated at the operating frequency. 3 GHz.

16

A ferrite material with magnetic saturation of 1750 Gauss was originally used, however,

when simulating in HFSS at the desired frequency region of3 GHz (S-Band) at no bias

the return loss (SI1) of the ferrite loaded waveguide recorded was -7 dB and the insertion

loss (S21) recorded at -5 dB. At other low biasing states the return and insertions loss

continued to worsen as may be seen in Table 3.1

1750 Gauss Ferrite Bias(kA!m) SlL(dB) Su (dB) 0 -7 -5 10 -6 -5 20 -8 -12 30 -7 -27

Table 3.1 Comparison between 0 - 30 kAlm for insertion and return loss of the ferrite loaded waveguide at 3 GHz.

So a new ferrite material must be substituted into the ferrite loaded waveguide, a ferrite

with magnetic saturation of 600 Gauss was best suited for the desired frequency region of

3 GHz, when simulating in Ansoft HFSS. A comparative study of the ferrite loaded

waveguide is done to evaluate the performance of implementing a 600 Gauss ferrite

material verses 1750 Gauss ferrite material in the S-band region of frequencies. As Table

3.2 depicts the 600 Gauss ferrite material shows improved results for insertion and return

loss over 1750 Gauss ferrite for 3 GHz at low bias.

17

600 Gauss Ferrite 1750 Gauss Fenite Bias(kAIm) Su (dB) Sn (dB) Sl1 (dB) S21 (dB) 0 -14 -0.6 -7 -5 10 -19 -0.6 -6 -s 20 -30 -0.8 -8 -12 30 -IS -1 -7 -27

Table 3.2 Comparison !able between 600 Gauss and 1750 Gauss ferrite at 3 GHz.

Therefore, using the information that was obtained by simulating the 600 Gauss ferrite

material, a new phase shifter design is needed to implement the 600 Gauss ferrite slab

material. The new proposed low-cost microstrip line-based ferrite phase shifter shown in

Figure 3.2 and Figure 3.3 was modified to improve performance at the low-bias region.

Ferrite slab (1.5 x 3 x 70 mm)

FIgure 3.2 Diagonally view of the proposed microstrip line-based ferrite phase shifter.

The new proposed design implemented a new ferrite material with magnetic saturation

of 600 Gauss, also all the microstrip lines were matched to 50 Q to ensure proper

impedance match. To produce circularly polarized waves the non-planar geometry was

18

kept similar to the previous non-planar phase shifter [10]. The dielectric constant of the

substrate was selected to be at 9.8, to minimize the discontinuities between the dielectric

substrate and the ferrite slab, the dielectric constant of the ferrite slab was also select at

9.8. The newly proposed phase shifter was designed to operate at 3 GHz (S-band). The

planar portion of the substrate was chosen to be 2 mm thick, which compared to the

previous non-planar phase shifter at 3.2 mm thick for the substrate, is slightly thinner.

The non-planar structure of the substrate extends an additiona13 mm which the ferrite

slab was embedded in the non-planar portion of the substrate, beneath the center

microstrip line. The ferrite slab has a length of70 rom, width of3 rom, and the thickness

of 1.5 mm. As was explained earlier the ferrite material was chosen to have a saturation

magnetization of 600 Gauss, a Lande g factorof2, anel anAH of SO Oe (4 kAlm).

Originally the three microstrip lines were chosen to be 3mm wide; however matching the

microstrip lines to 50 g requires the width of each microstrip line to be different

depending on the thickness of the substrate. Therefore the width of the center elevation

microstrip line was design to be 3 mm while the side traces of the non-planar structure

was design to be 2.5 mm and at the substrate level the width of the microstrip lines were

2 mm. Tapered transitions were used between the substrate level microstrip lines and the

non-planar level microstrip lines to ensure impedance matching.

19

15.5 cm

8. 5 mm 17.34 mm

2

Non-planar structure (3 x 5 x 85 mm)

Ferrite slab material (1.5 x 3 x 70 mm)

Qu rter-wave tran former width 5.2 mm

Fig. 3.3 Top view of the proposed microsuip line-based fe rrite phase shifter.

Instead of a trapezoid section to place the side microstrips as described in the previous

non-planar phase shifter design, vertical (90°) sidewall structure was implemented for

ease of fabrication, as shown in Figure 3.4. The feed-network design is similar to the

previous non-planar phase shifter due to the fact that it provides the ideal phase offsets of

+/- 90° to the outer two microstrip lines and divide the input power between the three

microstrip lines [10). A similar network was design at the ends of the microstrip Lines to

realign the pbases and recombine the power to produce one output signal.

20

5mm

• • , r 11111

3mm :l !lllll

.5mm

. ...".. :'l'"+

m

Figure 3.4 Cross section view of the proposed microstrip line-based ferrite phase shifter.

Simulation Results

Using Ansoft HFSS, the proposed microstrip line-based ferrite phase shifter was initially

simulated with no magnetic bias to confirm that the geometry itself would produce the

desired circularly polarized waves as shown in Figure 3.5.

Figure 3.5 Cross section view of the proposed microstrip line-based ferrite phase shifter. Observing the simulation, it verifies that the new non-planar structure does produce a circular polarization in the ferrite slab region.

21

Also to confirm if the proposed ferrite phase shifter had a low insertion loss (S21) and a

high return loss (SII) when no magnetic bias was applied to the proposed ferrite phase

shifter. Table 3.3 shows the simulation results of the proposed microstrip line-based

ferrite phase shifter at no bias. Where observing Table 3.3, it shows that the proposed

microstrip line-based ferrite phase shifter shows good results in return and insertion loss

when no magnetic bias was applied to the ferrite material.

Bias(kA/m) SII (dB) S21 (dB)

0 -35 -0.33

Table 3.3 Results of the proposed microstrip line·based ferrite phase shifter design return loss and insertion loss at no bias (0 kAlm)

The ferrite slab was biased in Ansoft HFSS by defining the net internal magnetic field

that biases the ferrite slab material. This internal bias field is similar to the effect of an

externally applied magnetic field for example a current-carrying coil by aligning the

randomly oriented magnetic dipoles in the ferrite to produce a nonzero magnetic moment

With Ansoft HFSS. the proposed microstrip line-based ferrite phase shifter was simulated

by running a parametric analysis that varied the magnitude of the internal magnetic bias

field in the ferrite region from 0 to 200 kAlm. A plot of the insertion loss (S21) shows

that at the low bias region the insertions loss (S21) is low and at the full bias region it

remains low as well. shown in Figure 3.6.

22

o

_.

-30 o

Mlcrostrlp Une Based Ferrite Phase Shifter InllGrtion Loss (1.5 x 3mmj

~ r ~

V

20 40 so so tOO t20 t40 tSO

InternaJ Magnetic Bias (kAIm)

180 200

FIg. 3.6 Insertion Loss (S21) vs. Internal Magnetic Bias of the new proposed microstrip line-based ferrite phase shifter at 3 GHz

However, in the middle region of biasing (40 - 80 kNm), they is a drop in the insertion

loss and the insertion loss becomes high. A plot of the return loss (SII) shows at the low

bias region and the full bias region the return loss becomes high. However in the middle

region (40 - 80 kNm) there is a peak as well and the return loss becomes low in that

particular region shown in Figure 3. 7.

This was suggested that they could be a problem with the software, and that Ansoft HFSS

in that region of bias is miscalculating the ferrite modeL Looking at the insertion phase

plot of the proposed ferrite phase shifter it can be seen that in Figure 3.8, that the

proposed ferrite phase shifter achieved a total phase shift of 314° between 0 kNm

(unbiased) to 200 kNm (full biased).

23

Microstrip Une Based Ferrite Phase Shifter Return Loss (1.5 x 3mm)

o

.. ·10

~ r--... ..... 1i ~

V V

fI

\ II v

o 20 40 BO 80 '00 '20 14" ,"" ,"" Internal Magnetic Bias (kAIm)

Figure 3.7 Return Loss (S,,) vs. internal magnetic bias of the new proposed microstrip line-based ferrite phase shifter at 3 GHz.

This equates to 143° per wavelength, which meets Lee and Strahan expectation of

obtaining 360° of phase shift in under a few wavelength. Table 3.4 shows the return loss,

insertion loss and the total phase shift (normalized to wavelength) of the proposed

microstrip line-based ferrite phase shifter design at no bias (0 kAlm) and at full bias (200

kAlm).

Bias Sl1 (dB) S21 (dB) Total Phase Shift (kA/m) (normalized)

0 -35 -0.33 143°/1..

200 -22 -0.29

Table 3.4 Results of the proposed microstrip line-based ferrite phase shifter design of return loss, insertion loss, and Iotal phase sbift (normalized 10 wavelength) at no bias (0 kAlm) and at full bias (200 kAlm)

24

...

...

) ... II.

.,.,

50

o o

MlcrostrJp Una Based Ferrite Phase Shlftar Insertion Phase

~ I

r /

7 /

2ll 40 flO 80 .,., .211 .40 "" .80

Internal Magnetic Bias (kAlm,

FIgure 3.8 Insertion Phase vs. intemaJ magnetic bias of the new proposed microstrip line-based fenite phase shifter at 3 GHz.

25

CHAPTER 4 FABRICATION OF MICROSTRIP LINE-BASED FERRITE

PHASE SHIFTER - 3 MM

After performing simulations using Ansoft HFSS, the next step is to fabricate the

proposed microstrip line-based ferrite phase shifter. The substrate and the non-planar

structure were made out of Rogers Corporation TMM10i material with Y2 ounce copper

rolled on the substrate, with a dielectric constant of9.8 and a dielectric loss tangent less

than 0.0001. A photo of the substrate is shown in Figure 4. J.

7.5 em

15.3 em

Figure 4.1 Substrate using Roger Corporation TMM I Oi material with Y, ounce copper rolled. Where the dimension for the substrate is 7.5 x 15 .3 em and thickness of 2 mm.

For the ferrite material a different type of ferrite was chosen (Saturation magnetization of

600 Gauss) to overcome the insertion loss difficulties described in Chapter 3. Nickel

Aluminum ferrite was chosen with a dielectric constant of9.8, a dielectric loss tangent of

0.0002, and a saturation magnetization of 600 Gauss. The ferrite was fabricated ITom

Countis Industries in Carson City, Nevada, they were chosen due to the fact that Pacific

26

Ceramics, Inc, which was the original manufacturer of the previous non-planar ferrite

phase shifter, did not supply or fabricated a ferrite with dielectric constant of9.8 and a

saturation magnetization of 600 Gauss. They referred Countis Industries to us, due to the

fact they could supply us with a ferrite material in which is a nickel aluminum ferrite slab

material type C-50A. Figure 4. 2 shows the substrate, the non-planar structure and the

ferrite slab material that was used in the newly proposed microstrip line-based ferrite

phase shi !ler.

FerTite Slab Material

Nickel Aluminum

Figure 4.2 Material for the newly proposed microstrip line-based ferrite phase shi fter, included in fi gure rrom clockwise left: ferrite slab, substrate, and non-planar strucrure.

The substrate of the newly proposed microstrip line-based ferrite phase shifter was cut

thanks to the help of Mr. Benjamin Respicio, Mr. Brian Kodama, and the rest of the staffs

27

at the Engineering machine shop located in University ofHawai'i at Manoa. The

substrate was cut using a table saw using a diamond saw blade, which is commonly use

to cut ceramic materials to prevent cracking or chipping of the dielectric substrate. The

non-planar stmcture for the newly proposed microstrip line-based ferrite phase shifter

was mi11ed using a C & C machine as shown in Figure 4.3. This process was needed to

create the slot in the non-planar stmcture so the ferrite slab can be inserted inside the non-

planar stmcture.

Non Planar Structure Rogers TMM 101

s.. = 9.8

5mm

Figure 4.3 Photograph of the new non-planar structure which was milled in the University of Hawai ' i at Manoa with a length of 5 mm, width of 5 mm and a height of3 mm.

Once the fabricated materials were completed, the materials were assembly together and

the ground plane was left on the substrate while the top portion of the substrate was etch

off using copper etchant. The microstrip lines were added to the assembled stmcture for

the feed network and non-planar stmclUre lines. Initially the microstrip lines for the feed

network were hand-cut from a rol1 of 3M smooth copper tape with conductive acrylic

28

adhesive. However, due to the lack of precisions from hand-cutting the copper tape, the

feed network was etched using a photo-laminate process, using a negative photo-resist

laminate. Contact lithography processes with a UV exposure system to create a photo-

resist mask so the feed network can be etch using a copper etchant. The feed network

mask pattern for the UV exposure system was generated using AutoCAD. Figure 4.4

shows the feed network after being etched using the photo-laminate, UV exposure

system, and the copper etch ant.

Figure 4.4 The feed network after photo-laminate, length of the 900 delay line is 31.575 mm and the length of _900 delay line is 49.575 mm.

The microstrip lines for the non-planar structure were hand-cut as well and the pattern

was generated using Agilent's ADS Momentum circuit-layout tool. The completed

microstrip line-based ferrite phase shifter prototype at 3 GHz is shown in Figures 4.5 and

Figure 4.6.

29

Figure 4.5 Complete prototype of microstrip line-based ferrite phase shifter, hand cut version of [he feed network

Fig4.6 Complete prototype of microstrip line-based ferrite phase shifter, photo-laminate version of the feed network

30

~

Side trace 3mm 2.

2mm • •

--Fig4.7 cross section view of micros trip line-based ferrite pbase shifter (3 mm), where the

dimension of the non-planar strucrure's cross section is 3 x 5 rom. The center trace width is 3.5 mm, side trace width is 2.5 mm, and the planar level trace is 2 mm.

Bias Coil and Experimental Results

Once the new prototype microstrip line-based ferrite phase shifter was completely

fabricated it was ready fore testing. To produce a magnetic bias field a bias coil was

needed, initially to speed the process of testing, the second bias coil from the previous

non-planar ferrite phase shifter was used [10]. To increase the magnetic bias compare to

the previous test set up, more layers ofturns was wound in the same direction, Figure 4. 7

shows the new bias coil with 7 layers each has 200 turns and hence the total number of

mrns is 1400 approxinlately.

31

Bias Coil

Figure 4.8 The bias coil after more layers ofmagnenc wire were hand wrap in the same direction as the previous. Bias coil has 7 layers each has 200 turns and hence the total number of turns is 1400 approximately.

Placing the new microstrip line-based ferrite phase shifter prototype inside the newly

modified with more layers bias coil and connecting the ports of the phase shifter to the

network analyzer and the coil to the DC power supply. The current in the bias coil was

increased to full bias and back down; the polarity of the coil was reversed to obtain

negative current from the DC power supply. The current was increased in the negative

direction until full reversed bias was reached, after which the current was once again

reduced to zero. After testing the device it was observe that the microstrip line-based

ferrite phase shifter was producing phase shift as the current in the coil changed.

Although adding more layers to the bias coil , the microstrip line-based ferrite phase

shifter still did not provide adequate amount of phase shift. A screen shot of the return

loss (S II). insertion loss (S21). and the insertion phase at 30Hz when no bias is applied to

the bias coil is shown in Figure 4.9. While a screen shot of the return loss. insertion loss.

and the insertion phase at 30Hz when a bias of2 .65 A is applied is shown in Figure

4.10.

32

>3: 3.000 GHz 113.0°

8 21 phase at 0

1----1----1----, bias, 113·

Figure 4.9 Screen shot or the new microstrip line-based ferrite phase shifter (3 mm), return loss, insertion loss and the insertion phase at no bias. S" magni tude is in orange (I), S" magnirude is in the blue line (2), and S21 phase is in the orange, bottom part (3). Top part of the figure is for the magnirude ofS'1 and Si lo while the bottom part is for the phase ofS'I '

Looking at the screen shot the prototype microstrip line-based ferrite phase shifter only

obtain close to 80 of phase shift. One solution to this problem is to increase the current

on the bias coil so a new power supply was obtain with a maximum current power of 10

A. So attaching the bias coil, to the new DC power supply, and increasing to the full bias

current of 10 A and going back down to zero and reversing the polarity of the coil, from

the DC power supply. A screen shot of the prototype microstrip line-based ferrite phase

shifter at 2.7 GHz was obtain at zero bias and at full bias of 10 A, shown in Figure 4.11

showing zero bias and Figure 4. J 2 showing at bias of lOA.

33

>3: 3.000 GHz 121 .30

5 21 phase at 2.65A, 121 .3°

Figure 4.10 Screen shot of the new microstrip line-based ferrite phase shifter (3 mm), return loss, insertion loss and the insertion phase at 2.65A. S I1 magnitude is in orange (I), S'I magllitude is in the blue line (2), and S" phase is in the orange, bOllom pan (3). Top part of the figure is for the magnitude 0[S21 and Silo while the bOllom pan is for the phase ofS2\.

>1 : 2.72 GHz -15.90 dB >2: 2.72 GHz -1 .100 dB

with new DC power -51.68°

Figure 4.1 1 Screen shot of the new microstrip line-based ferri te phase shifter (3 mm), return loss, insertion loss and the insertion phase when a new DC power supply added to the test setup at no bias. SI1 magnitude is in orange ( I), S" magnitude is in the blue line (2), and S21 phase is in the orange, bOllom pan (3). Top part of the figure is for the magnitude o[S2\ and SI1, while the bOllom part is for the phase of S2\ .

34

>1: 2.72 GHz -14.37 dB >2: 2.72 GHz -1 .544dB

E3E3~8~~~f~i§t~~S~2~, :p~h:a:se at 10A with ~~E~~~~~~~~~~~~tn~e~w~D~c~power supply, ~ -34.31'

>3: 2.72 GHz -34.31 °

Figure 4.12 Screen shot of the new microstrip line·based ferrite pbase shifter (3 rnm), rerum loss, insertion loss and the insertion phase at lOA wben a new DC power supply is added in the test serup. S" magnitude is in orange ( I), S" magnirude is in the blue line (2), and S" phase is in the orange, bottom pan (3). Top pan of the fi gure is for the magnirude ofS" and S" , while the bottom part is for the phase of S".

Observing the results obtained from the measurements, it was found that with the new

DC power supply and applying the maximum current bias to the bias of 10 A coil, the

prototype microstrip line-hased ferrite phase shifter obtain a little over 17° of phase shi ft.

This is inadequate for the amount of phase shift needed. Another solution to this

problem, of the insufficient amount of phase shift, is to redesign a new bias coil.

In designing a new bias coil, increasing the amount oftums per cm, while making sure

that the size and resistance of the coil is not increased, is one of the main goals in

designing a new bias coil. For the microstrip line-based ferrite phase shifter the area of

interest for the coil is in the ferrite region, therefore the substrate was cut to allow a bias

coil to be made around the ferrite region. Using 22 A WG magnetic wires with thin

enamel-insulator for the bias coil, Figure 4.13 and Figure 4.14 show the cut substrate

35

where the cut region is where the bias coi l will be, by wrapping the 22 A WG magnetic

wires around using a cardboard roll over the ferrite region.

15.3 em

Feed networks Figure 4.13 The top view of microstrip line-based ferrite phase shifter (3 mm) when the

substrate is cut to fit the new bias coil around the ferrite region

Figure 4.14 Another view of microstrip line-based ferrite phase shifter (3 mm) when the substrate is cut to fit the new bias coil around the ferrite region

36

The microstrip line-based ferrite phase shifter's bias coil was hand wound in the same

direction, as the previous coil , in the direction of propagation. The compact size of the

new bias coil allows for more layers without increasing size and resistance of the bias

coil. The new bias coil allows for more magnetic fields in the ferrite region, Figure 4.15

and Figure 4.16 shows the complete microstrip line-based ferrite phase shifter prototype

with the new bias coil.

Bias coil

I

Figure 4.15 The complete microstrip line-based ferrite phase shifter prototype (3 mm) with the new bias coil around the ferrite region

After fabricating the new bias coil the newly microstrip line-based ferrite phase shifter

prototype was measured, screen shots were obtain to see how much phase shift was

produce from the prototype phase shifter. Figure 4.17 shows the insertion loss, return

loss, and the insertion phase of the new prototype phase shifter at 3.16675 GHz when

zero bias was applied to the bias coil.

37

~Cc)8)(ial in Coaxial out

Figure 4.16 The side view of complete microstrip line-based ferrite phase shifter prototype (3 mm) with the new bias coil around the ferrite region

Start

>1 : 3.16675 GHz -28.42 dB >2: 3.16675 GHz -1 .728dB

>3: 3.166750 GHz -9.471 0

S 21 phase at 0 bias with new bias coil, -9.471 0

Figure 4.17 The screen sbot of the insertion loss, return loss, and insertion phase of the new microslrip line-based ferrite pbase shifter (3 mm) with tbe new bias coil at 3.1 6675 GHz when no bias is applied. S" magnitude is in orange (1), S" magnitude is in the blue line (2), and S" phase is in the orange, bOllom pan (3). Top pan of the figure is for the magnitude ofS" and S", while the bOllom pan is for the phase ofS" .

38

Figure 4. /8 shows a screen shot of the insertion loss, return loss, and insertion phase of

the prototype phase shifter at 3.16675 GHz when full bias was applied to the new bias

coil. The total phase shift that was obtained from the new microstrip line-based ferrite

phase shifter prototype with the new bias coil was approximately 40° of phase shift.

With the new bias coi l it shows a vast improvement compare to the previous cases while

maintaining a good insertion and return loss values, however it is sti ll provided a very

inadequate amount of phase shift. Therefore another solution is needed to improve the

amount of phase shift for this device.

>1 : 3.16675 GHz -25.24 dB >2: 3.16675 GHz -1.230dB

>3: 3.166750 GHz 29.64°

8 21 phase at 10A ~_+-_+-_+~""'OIII!!!.~, with new bias coil,

29.64° ~op '

Figure 4.18 The screen shot of the insertion loss, return loss, and insertion phase of the new microstrip line-based ferrite phase shifter (3 mm) with the new bias coil at 3.16675 GHz when full bias is applied. S" magnitude is orange line (I ). S21 magnitude is the blue line (2), and S21 phase is in the orange, botlom pan (3). Top part of the figure is for the magnitude OfS21 and S Ilo whi le the bottom part is for the phase OfS21.

39

CHAPTERS D ESIGN AND SlMULATlON OF MiCROSTRIP LINE-BASED FERRITE PHASE

SHIFTER -S MM

Due to the insufficient amount of phase shift from the previous prototype as explained in

Chapter 4, it was suggested that we change the size of the ferrite slab in the ferrite phase

shifter region. This is expected to increase the sensitivity of the phase change and

possibly give the 3600 that is needed for this project. Increasing the size of the ferrite rod

is also expected to reduce the size of the bias coil, therefore minimizing the fabrication

cost. Using available ferrite materials a ferrite slab with dimension of3 x 5 x 70 mm,

which is almost twice the height and width of the original ferrite slab, was simulated in

Ansoft HFSS. The non-planar structure and the feed network was modi fied to install the

new ferrite slab material and as well as to maintain circular polarization. Figure 5.1

shows the cross section ofthe new design of the microstrip line-based ferrite phase

shifter, where the ferrite slab is increase and the non-planar structure is modified to install

the new ferrite slab. As discussed earlier the feed network was modified to maintain the

phase offset of +/-900 to the outer two microstrip lines as well as adjust for the non-

planar structure. Figure 5.2 shows the feed network in Ansoft HFSS, where the length of

lines for the feed network was modified.

40

7mm

4.5 m

5mm

Fig5.l The cross section of the new design of the microstrip line-based ferrite phase shifter (5 rrun) with a larger ferrite slab cross section of 3 x 5 mm

tr""'",,, 2.5mm

transformer

Figure 5.2 The feed network in Ansoft HFSS of the new design rnicrostrip line-based ferrite phase shifter (5 rum) with a larger ferrite slab 3 x 5 mm.

41

Once the non-planar structure and the feed network was modified, the complete

microstrip line-based ferrite phase shifter was ready to be simulated in Ansoft HFSS,

Figure 5.3 and Figure 5.4 shows the complete design of the new microstrip line-based

ferrite phase shifter with the increase ferrite slab cross section (3 x 5 mm).

Ferrite slab (3 x 5 x 70 mm)

7.5cm

Non-planar structure (4.5 x 7 x 85 mm) Figure 5.3 The complete design of the new microstrip line-based ferrite pbase sh.ifter (5 mm) with

a larger ferrite slab 3 x 5 mm.

42

15.5 cm

Non-planar structure (4.5 x 7 x 85 mm)

----+-I=or'rito slab material (3 x 5 x 70 mm)

7.5 em Figure 5.4 Top view of the complete design of the new microstrip line-based ferri te phase shifter

(5 mm) with a larger ferrite slab 3 x 5 mm.

Simulation Results

With Ansofi HFSS, the proposed ferrite phase shifter was simulated by TUIU1ing a

parametric analysis that varied the magnitude of the internal magnetic bias field in the

ferrite region from 0 to 200 kAlm. A plot of S21 insertion loss shows that at the low bias

region the insertions loss (Sll) is low and at the full bias region it remains low as well,

shown in Figure 5.5.

43

Mlcrostrlp Line Based Ferrite Phase Shifter Insertion Loss (3 x 5mm)

o

~ / \; ..

f\ -;:; ·10

if - -16

i·~ ·26

o 20 40 00 80 100 120 140 100 180 200

Internal Magnetic Bias (kAIm)

FIgure 5.5 The graph of the insertion loss 8" vs. internal magnetic bias at 3 GHz

Observing the insertion loss of the new microstrip line-based ferrite phase shifter, it can

be seen that in the insertion loss at the 40 - 80 kAlm region there is a drop in that region.

Also in the return loss graph there is a jump in the 40 - 80 kAlm regions as well shown in

Figure 5.6. One speculation that was made was the software, Ansoft HFSS, ferrite model

was incorrect and that it was miscalculated in that region.

44

Mlcrostrlp Une Based Ferrite Phaee Shifter Return Loss (3 x Smm)

o

.. ·10

·1. 1\

i- _ A 1/\

vvv '" VV"\ fvJ\ r1V "\ r'\ /\ ("v V '\ N V

I:;

If V

-so o 20 40 60 60 100 120 140


FIgure 5.6 The graph of the return loss 8,. vs. internal magnetic bias at 3 GHz

V v

160 160

However, observing the insertion phase of the new microstrip line-based ferrite phase

shifter, it can be shown that the insertion phase is much larger than the previous design

when the ferrite slab was 1.5 x 3 mm. This solves the problem ofless phase shift in the

lower bias region and therefore decreases the size of the bias coil; Figure 5. 7 shows the

graph of the insertion phase of the new microstrip line-based ferrite phase with ferrite

slab 00 x 5 mm. Also Table 5.1 shows the value of the return and insertion loss at zero

bias and the return loss, insertion loss, and insertion phase when at full bias of 200 kAhn.

In Table 5.1 it shows a total phase shift of 1028° which is approximately 467° in a

wavelength. Therefore this improves the amount of phase shift in the lower bias region,

provides 360° of phase shift, and improves the size of the bias coil. So the next step will

45

200

be fabrication of the new proposed microstrip line-based ferrite phase shifter prototype (5

mm).

Bias (kA/m) Sl1 (dB) S21 (dB) Phase Shift

0 -23.54 -0.44 1028° or 200 -26.20 -0.28 467°/') ..

.. Table 5.1 Table of the new IDlcrostrip line-based ferrite phase shifter (5 mm) inSertion loss, return loss, and insertion phase at 0 bias and at full (200 kA/m) bias

1200

1000

200

o o

Mlcrostrlp Une Based Ferrite Phase Shifter Insertion Phase (3xSmm)

( )

r

/ 2D 40 80 80 100 120 140 180


Figure S.7the graph of the insertion phase S21 vs. intemaI magnetic bias at 3 GHz

46

'80 200

CHAPTER 6 FABRICATION OF MICROSTRIP LINE-BASED FERRITE

PHASE SHIFTER -5 MM •

Observing the simulation results of the new microstrip line-based ferrite phase shifter,

with the ferrite slab cross section of3 x 5 nun, shows much improvement to the previous

design with a ferrite slab of 1.5 x 3 mIn. To verify the simulation results, fabrication of a

new design of the mjcrostrip line-based ferrite phase shifter is needed. The substrate and

the non-planar material were fabricated using Rogers Corporatjon TMM I Oi with a rolled

copper clad of Y, ounce copper. The substrate, for the bias coil region, shown in Figure

6.1 was cut using a diamond saw blade.

Figure copper clad of Y, ounce of copper. around the ferrite region.

4.3cm III

I I 4.1 em

Corporation (TMM I with a rolled The substrate was cut so the new bias coil can be hand wrap

47

The non-planar structure, insening the larger ferrite slab of3 x 5 mm, was milled using a

C & C machine, shown in Figure 6.2. Both substrate and non-planar structure was

fabricated thanks to the help of Mr. Benjamin Respicio, Mr. Brian Kodama, and the rest

of the staffs at the engineering machine shop located in University ofHawai'i at Mllnoa.

7nvn

85mm

Figure 6.2 The new non·planar structure for the larger ferrite slab of 3 x 5 mm, material use is fTom Roger Corporation (TM.!VI Wi)

The ferrite slab material that is used is a nickel aluminum type C-50A with the same

dielectric constant and magnetic saturation as the previous design (3 mm). The ferrite

slab was fabricated from Countis Industries in Carson City, evada; Figure 6.3 shows

the larger ferrite slab material. The feed network was fabricated using the photo-

laminate process explain earlier in Chapter 4, where a negative photo-resist laminate was

apply to the copper substrate and exposure to UV light to create a photo resist mask, the

unwanted copper is etched using a copper etchant, the fabricated feed network can be

shown in Figure 6.4.

48

Smm •

70mm •

3 mm, hALrtht

Figure 6.3 Photograph of the new ferrite slab material, nickel aluminum from Countis Industries, magnetic saturation of 600 Gauss. A larger ferrite dimension than the previous with 3 x 5 mm cross section

Figure 6.4 The feed network after photo-laminate process and copper etch

Once all the materials were fabricated, the new microstrip line-based ferrite phase shifter

was put together, ready to be tested. Figure 6.5, Figure 6.6, and Figure 6.7 shows

different views oftbe complete microstrip line-based ferrite phase shifter prototype

without the bias coil.

49

Figure 6.S The complete microstrip line·based ferrite pbase shifter prototype (5 mrn) without the bias coil

The bias coil were hand wound around the ferrite region of the microstrip line-based

ferrite phase shifter prototype, 22A WG magnetic wires were used for the bias coi l,

Figure 6.8, Figure 6.9, and Figure 6.10 shows different views of the complete microstrip

line-based ferrite phase shifter prototype with the bias coil. The bias coil is needed to

apply an external magnetic field to the ferrite slab material. The bias coil for the

prototype microstrip line ferrite phase shifter had about 900 turns ofan average diameter

of5.3 cm and length of6.7 cm.

50

length 48.075 mm

"-

8m~

Figure 6.6 Another view of tbe complete microstrip line-based ferrite phase shifter prototype (5 mm) without the bias coil

5.25mm 2mm-+ +-

Figure 6.7 Top view of the complete microstrip line-based ferrile phase shifter prototype (5 mm) without the bias coil

51

--

Figure 6.8 cross section view of the complete microstrip line-based ferrite phase shifter prototype (5 mm) without the bias coil

Substrate width 7.5 em

Figure 6.9 The complete microstrip line-based ferrite phase shifter prototype (5 mm) with the bias coil

•

52

. .. \ . •

Figure 6.10 Another view of the complete microstrip line-based ferri te phase shifter prototype (5 rom) with the bias coil

the bias coil

Length 6.7 em

complete microstrip line·based ferrite phase shifter prototype (5 mm) with

53

CHAPTER 7 EXPERIMENTAL RESULTS OF

MICROSTRIP LTh'E-BASED FERRITE PHASE SHIFTER -5 MM

Once the microstrip Line-based ferrite phase shifter prototype (5 = ) was completed,

using an Agilent E8364B network analyzer and a DC power supply to apply current to

the bias coil, it was tested and measure to verify that the simulation was accurate and that

the prototype could provide 3600 of phase shift. When measuring the micros trip Line-

based ferrite phase shifter prototype (5 mm), screen shots was capture at zero bias and at

full bias, here it provides that the prototype phase shifter does provide more than 3600 of

phase shift, as shown in Figure 7.1 and Figure 7.2. Where Figure 7.1 shows when no

current is apply to the bias coil and Figure 7.2 is when at the max current was apply to

the bias coil which gives full bias.

. Statua 0i1 s c~ 2-P SOLT La.

Figure 7.1 Screen shot of new microstrip line·based ferrite phase shifter prototype (5 mm) when no bias is applied. In the figure SII (yellow) and S21 (blue). The top part of the figure is for the magnitudes, while the bottom part is for the phases.

54

Stotuo Oi, : .;S ... 21J....._~~ C" 2-P SOlT LCl Figure 7.2 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) when full bias is

applied. In the figure SII (yellow) and S" (blue). The top part of the figure is for the magnitudes, while the bottom part is for the phases

From Figure 7.1 and Figure 7. 2 it may be noted that the phase values start with about

-131.7° in the phase ofS21 (zero bias), continue to +180° (total of321.7°) before the

network analyzer scale transition from + 180° to _180° shown in Figure 7.3 and Figure

7.4, and then the phase continues to change with the increase in bias from -180° to a final

value of 177.8° (total of357.8°) for a total phase change of679.5°. Figure 7.3 shows

screen shot of the S-parameters before the phase transition (+180° to -180°) while Figure

7.4 shows the screen shot after the phase transition. From these figures it may be noted

that the phase values reponed in this figure starts with about -131. 7° in the phase of S2h

continue to + 180° before the false transition from +180° to -1 80° and continues to change

with the continued increase in the bias current. In other words, the false transition in

55

phase from + 1800 to -1800 is accounted for when presenting the results in Figure 7.12.

StatlA CH 1 C' 2·P SOL T lCL

Figure 7.3 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 rom) before pbase transition. In the figure S" (yellow) and S" (blue). The top part of the figure is for the magnitudes, while the bottom pan is for the phases

. Statui CH 1 ~ 2·P SOlT lO-

Figure 7.4 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) after phase transition. In the figure S" (yellow) and S" (blue). The top part oftbe figure is for the magnitudes, while the borrom part is for the phases

56

Another experimental test was done to show at no bias and when at a certain bias, the

phase shifter achieved 3600 of phase shift. Screen shots were capture at zero bias where

at the starting phase point of -1300 was recorded and at a certain bias we obtain 3600 of

phase shift, which the phase point attain was at -131 0. In Figure 7. 5 shows the starting

phase of -1300 at zero bias and Figure 7.6 shows the end phase point at -131 0 when

biasing up to 3600 of phase shift.

Stolul CH 1: .,. S~21,-__ ~~C,-,· 2.p SOlT lCL Figure 7.5 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 mm) when no bias

is applied. in the figure SII (yellow) and S" (hlue). The top part oftlle figure is for the magnitudes, while the bonom part is for the phases

Taking phase measurement from our new microstrip line-based ferrite phase shi fier

prototype at multiple bias points, a comparative analysis was done between simulation

57

and experimental results. Figure 7.7 shows the experimental results of the return loss

(S II) at multiple bias points, where base on the number of turns in the bias coil and the

applied bias current, it is estimated that phase shifter was bias up to 100 Wm and in

Figure 7.8 shows a comparison between the simulation return loss and the measured

return loss. Observing Figure 7.8, it can be shown that the simulation and the measured

values do somewhat match and their trends correlate.

Figure 7.6 Screen shot of new microstrip line-based ferrite phase shifter prototype (5 rom) when 360' is achieved. In the figure S1I (yeUow) and S'I (blue). The top part of the figure is for the magnitudes, while the bottom part is for the phases

Also shown in Figure 7.9 is the experimental result of the insertion loss of the microstrip

line-based ferrite phase shifter prototype, where multiple bias points were taken when

58

measuring the devices. In Figure 7.10, it shows the simulation results with that of the

experimental results, where the simulations and the experimental results somewhat

matches and the trends correlate well. However, in the experimental results there is still a

drop in insertion loss in the middle region of biasing, where assumption was that Ansoft

HFSS was incorrectly calculating the ferrite model. Consequently, the simulation and

experimental results matches, therefore Ansoft HFSS was correctly calculating the ferrite

model. Another assumption that can be made for this phenomenon is probably due to the

type of ferrite being use that could cause the insertion loss to drop during those biasing

range.

Mlcrostrlp Une Based Ferrite Phase Shifter Return Loss (Measured)

• ..

·1.

~ / --- " { \.J

• I • 20 30 40 50 60 70 60 .. 100

Internal Magnetic BIBa (kAIm)

Figure 7.7 Experimental return loss (SII) results of the microstrip Jine..based fernie phase sbifterprototype (S mm) vs. internal magnetic bias.

59

Return Loss (511) measured VB. simulation

D

-10 . ........ . •

A • .. ...... .. .. .. .. .. • • .. .... .. .. .. .. .... .. .. .. .. .. • • •

-1.

( \/\ • • . - ~ ..... • • 'V" VV

'"""' I V V"\

V '\ '\ \r

V ....

D 10 3D 4D 6D 7D 6D


••• S11 Measured -S11 Simulation

FIgure 7.8 Comparison between simulation return loss results and experimental return loss results of the new microstrip line·based ferrite phase shifter (5 mm).

Mlcrostrlp Une Based Ferrite Phase Shifter Insertion Loss (Measursd)

D

"'" \ \ (

-10

\ \ / V

c---

-3S

D 10 2D 3D 4D 6D 60 7D " '" 100


Fignre 7.9 Experimental insertion loss (Sal) results of the microstrip line·based ferrite phase shifter prototype (5 mm) vs. intemaJ magnetic bias.

60

Insertion Loss (S21) measured vs. simulation

o _ .. _---------- .. - ....................

/" "'" .

• • •

\ •

/ ,

1:\ .... ....... \ ,J '. \ • • • • • • • •

• • • • • •

-10

I -3 :E -15

i :Iii -20

V • \1 • • • • • • • • -

o 10 20 40 so so 70 80 90

Internal Magnetic Blaa (kAIm)

•• - S21 Measured -821 Simulation

Figure 7.10 Comparison between simulation insertion loss results and experimental insertion loss results of the new microstrip line-based ferrite phase shifter (5 mm)_

The insertion phase was also recorded with multiple bias points so that a comparative

analysis can be made from the simulation results and the experimental results. Figure

7.11 shows the insertion phase of experimental result from the microstrip line-based

ferrite phase shifter prototype when measuring at multiple bias points_ Observing Figure

7.11, it shows that the prototype microstrip line ferrite phase shifter obtained a total phase

shift of679.5° which approximately 3090 of phase shift per wavelength. Figure 7.12

shows the comparative graph of the simulation insertion phase with that of the

experimental insertion phase of the phase shifter prototype. Observing Figure 7.12, it

shows that the experimental insertion phase is less than that of the simulation insertion

phase; This is probably due to the fact that magnetic field isn't penetrating the ferrite

61

correctly, as compare to simulation setup where Ansoft HFSS internally bias the ferrite.

• aoo

700

600

200

100

o o

Mlcrostrlp Une Based Ferrite Phase Shifter Insertion Phase (Measurad)

(

/ /

/ /

/ ---10 20 30 40 61) 70 B1I

InI8maI Magnetic Bias (kAIm)

90 100

Figure 7.11 Experimental insertion phase (821) results of the microstrip line·based fenite phase shifter prototype (5 mm)

This could be various factors that could cause the magnetic field to penetrate incorrectly,

which causes the difference in the amount of phase shift; one factor could be the copper

traces could be affecting the magnetic field from penetrating the ferrite slab. In Figure

7.12, simulation and experimental results does somewhat match and the trends do

correlate well, however there is a shift in the measurement result with a shift toward

higher values of the measured bias. Figure 7.13 shows the return and insertion loss for

both simulation and experimental results.

62

Phase Measured vs. Simulation

1000 900 800

I 700 600 500

---• Total Phase Shift @ 3.3 GHz: 679.5° I' • Length: 2.21. /

• Experimental phase shift ./ ' ..... - .. , per wavelength: 309°n.. /' •

J 400 300 200 100

0

• • • Phase Measured I I

J , - Phase Simulation / • •

.. _-:--::- .... .. .. .... .. eo

o 20 40 60 80

Bias (kAfm)

FIgure 7.12 Comparison between simulation insertion phase resuIts and experimenta1 insertion phase results of the new microstrip Jine-besed ferrite phase shifter (5 nun).

So therefore a study must be perform to explain the ferrite biasing issue to solve the

difference between simulated and measured biasing. This can be explained as due to the

fact that the value of the kNm bias used in the HFSS simulation as assigned directly to

the ferrite rod, while the measured bias value used in reporting the experimental results

are based on measurement of the input current to the coil and multiplying it by the

number oftums.

63

o -5

-10

~-15 --20 .:l :e -25

&-30

:1\1-35

-40

45

-50

Measured vs. Simulation

.. _. . --....... ~ . /"

'\ .~ I .e_e \ rx- .. ~ I , .- ... ~ ~ • , ,.--........ •

I • \ 1\ 'rI • f - -- " '-' VV "-.,. I vV"'\, V '\

•• 811 measured •• 821 measured '\ - 811 simulation -- 821 simulation

\('" v

o 20 40 60 80 Blas(kAIm)

Figure 7.13 Combine comparison between simulation return and insertion loss results and expetimentaJ return and insertion loss results of the new microstrip line-based ferrite phase shifter (S mm).

This is certainly different (larger) than the actual bias value at the location of the ferrite

rod due to factors such as the finite length of the coil and associated magnetic flux

leakage as well as the interference caused by the presence of the three microstrip lines

and ground plane around the ferrite rod. If such factors are taken into account, an

effective value of the experimental bias is expected to be lower than the reported value

and a reasonable agreement between the experimental and simulation results may be

derived from Figure 7.12 and Figure 7.13. To help estimate an effective value for the

experiment bias case that should be compared with the directly applied value in the HFSS

simulation. Figure 7.14 shows a simple bias coil design in Ansoft HFSS. The bias coil

was design with 20 turns and a length of3 em., applying a current of2 A to the simple

bias coil. As HFSS does not simulate DC cases, a frequency of 100 kHz was used in this

simulation. Theoretically, the magnetic field obtain from multiplying the number of turns

64

by the current applied and dividing over the length of the bias coil (i.e. assuming closely

wound infinitely long coil) should be 1333 Aim as shown in Figure 7.14. However,

simulating the bias coil in HFSS the simulated magnetic field obtained from the bias coil

was recorded at 1050 Aim as shown in Figure 7.15. Therefore dividing the value from

the simulated H-field with that of the value of the theoretical H-field an internal to

external H-field ratio of 0.78 was calculated.

d = 3 cm

N = 20 turns

1 = 2 A

icrostrip Lines

Theoretical Magnetic Field

H = NII( d) = 1333 Nm Figure 7.t4 Simple bias coil design in Ansoft HFSS, the bias coil was designed with 20 rums and

length of 3 em and apply a current of 2 A. A theoretical magnetic field of 1333 AIm if calculating H = NlJd.

Simu lated Magnetic Field H = 1050 AIm

Simulated Magnetic Field Theoretical Magnetic Field = 0.78

Internal to external H-field ratio = 0.78

Figure 7.15 Simple bias coil simulated in HFSS, where it was observed that the simulated magnetic field of 1050 AIm was simulated in the bias coil. Dividing the simulated H-field with that of the theoretical H-field; an internal to external H-field ratio of 0.78 was calculated.

65

Measured ¥s. Simulation with ratio Included

O~~~.~.~ .. ~.~ .. ~ .. r.~.~.~~~~~~----------------~

~~--------------------------~~~----------------~

·'0 +------- -----------------------------1~------h~r=_=:.'+I

·.5 ~--------------------------c_;_.----=----v.=_+--___;~--t:+_'1

l~+-------~~~~------------------~~~~~~~~~ GO

~~5+--~~~~--~-,~~~.----------7------~~~--~~ c I ~ +--------------=---- ------""'"""--I"'.d'------------1

~+___c-------------------~------------------------~ - Sll Simulation

---S21 Simulation

•••• Sll Measured with ratio

.... S21 Measured with ratio ~~~========~====~==~~----~----~----~--~

o w ~ ~ ~ 00 00 ~

Magnetic Bias (kAIm)

FIgure 7.16 Combine comparison between simulation retmn and insertion loss results and experimental retmn and insertion loss results when applying the internal to external H-field ratio of the new microstrip line-based ferrite phase shifter (5 mm). Where the experimental results and the simulation results are well match and show good agreement with each other.

So applying this ratio to the experimental measurements, shown in Figure 7.12 and

Figure 7.13, we can see in Figure 7.16 that the insertion and return loss for the

experimental results show good agreement and well match to the simulation results.

Thus proving that the microstrip line-based ferrite phase shifter prototype does match

well with the simulation results and they show good agreement with each other. Figure

7.17 shows the insertion phase when applying the ratio with the experimental results; it

also shows good agreement and is well match with the simulation results. Also the

obtained experimental results indicate that the microstrip line-based ferrite phase shifter

prototype does achieve a total phase shift of 679.5° over its entire length, which is

66

equivalent to approximately 100 /mm or 309° of phase shift in an approximate

wavelength, thus exceeding our expectation.

Measured V8 Simulation Insertion Phase with ratio Included

".., --- -

1000

/

:/-----1

200

D

(7 -821 Phase SImulation ) , . - - - ·821 Measured WIth

ratio ~ .... , ..... _.- ... . . -.. ~ .. ~ ..

o 10 ~ ~ ~ ~ ~ ~

Magnetlco Bias (kAIm)

I

Figure 7.17 Combine comparison between simulation insertion phase resuIts and experimental insertion phase when applying the intemal to external H-field mtio to the experimental results of the new microstrip line-based ferrite phase shifter (5 mm). The experimental and simulation results are well match and show good agreement with each other.

67

CHAPTERS CONCLUSION AND FuTuRE WORKS

A low-cost microstrip line-based ferrite phase shifter was designed and fabricated at the

Hawai'i Center for Advanced Communications (HCAC) located in the University of

Hawai'i at Milnoa. This phase shifter was redesigned from the previous non-p1anar

ferrite phase shifter fabricated in 2003 [10]. Large insertion and return loss values at the

low bias region were identified in the earlier design and the design did not achieve the

desirable 3600 of phase shift. The new microstrip line-based ferrite phase shifter was

designed to improve insertion and return loss by implementing a new ferrite material with

a magnetic saturation of 600 Gauss instead of 1750 Gauss. The new microstrip

transmission lines were all matched to 50 Q. The microstrip lines reduced the weight and

size of the device as well as the manufacturing cost. The ferrite slab provided the

controllable phase shift through adjusting the DC current in the magnetic bias coil.

Simulation results showed that it is possible to achieve a phase shift of 4670 in an

effective wavelength using the new micrsotrip line-based ferrite phase shifter with the

ferrite slab of3 x 5 mm. The insertion and return losses were also improved in the low

bias region, at 0 bias SII = -23.54 dB and S21 = -0.44 dB (see Chapter 5). With the

encouraging simu1ation results, a prototype phase shifter was fabricated to help

experimentally verify the simu1ation results. The new microstrip line-based ferrite phase

shifter prototype was fabricated using Rogers Corporation TMMlOi for the substrate and

non-planar structure. The substrate was cut to the desired dimension of7.5 em x 15.3 em

and the non-planar was milled using a C & C machine with a dimension of 5 x 7 x 85

68

mm. A nickel alwninum ferrite slab material from Countis Industries was used for the

ferrite material. The feed structure was etched using a photo-laminate process and for the

microstrip lines, copper tape was used. The magnetic bias coil was hand wrapped around

the ferrite region of the prototype with approximately 900 turns with an average diameter

of 5.3 em and length of 6.7 em. Once the bias coil was fabricated; the prototype was

ready to be tested in the microwave network analysis lab in the Hawai'i Center for

Advanced Communications facilities. Once tested the micro strip line-based ferrite phase

shifter prototype (5 mm) results were recorded. Multiple bias points were recorded to

compare the experimental results with that of the simulation results, as may be seen from

the results reported in Chapter 7. An additional study of the bias coil provided an

internal to external H-field ratio. Applying this ratio to the experimental results showed

that the simulation results of the microstrip line-based ferrite phase shifter (5mm) does

match up very well with that of the experimental results; the obtained experimental

results also indicate that the fabricated prototype does provide 3090 of phase shift in a

wavelength. Therefore the low-cost microstrip line-based microstrip line ferrite phase

shifter achieved the goals of being low-cost, light weight, compact in size and providing

an approximately 3600 of phase shift.

Future work that may be needed to further improve the phase shifter design includes the

redesign, simulation, and fabrication of a new prototype with an increase in the size of

the ferrite slab material. This is expected to improve the sensitivity and hence make it

possible to provide 3600 within the lower bias region thus reducing the size of the bias

69

coil. A comparative simu1ation analysis was conducted to examine this approach where

the ferrite slab was simulated in different cross section dimensions. As Figure 8.1

depicts, an increase in the ferrite cross section of 7 x 9 mm shows an increase

performance in phase shift in the lower internal magnetic bias region. Observing at a bias

point of30 kNm, ferrite slab material's cross section of7 x 9 mm had a phase shift of

approximately 1250 and comparing to ferrite slab material's cross section of5 x 7 mm

where the phase shift is approximately 750• Figure 8.2 and Figure 8.3 show the design of

the proposed ferrite phase shifter when the ferrite slab material's cross section is

increased to 7 x 9 mm. Figure 8.1 shows that when increasing the size of the ferrite slab

material cross section, the microstrip line-based ferrite phase shifter will achieve 3600 of

phase shift at a much lower internal magnetic bias region than the prototype microstrip

line presented in this thesis. Therefore with the increase in sensitivity the size of

magnetic bias coil is expected to be reduced.

P~Shffi8rCom~n

'" -Ferrite - 1.5mm x 3mm .. .... Ferrite .. 3mm x Smm I I- ~Ferrlte .. Smm x 6mm -A-Ferrite .. 6mm x 7mm j r- - Ferrite .. 7mm x 9mm

/ '"

300 / /

c-- / /

/ --=

f~ 2QO

'60

". .. ---------:: ... . . ~

........ . .. -". .. .... 0& ....

• • " " " 30 " .. Figure 8.1 Comparison between ferrite cross section where ferrite cross section of7 x 9 nnn shows a

\'lISt improvement of phase shift compare to ferrite cross sections of smaller dimensions.

70

Figure 8.2 Future microstrip line-based ferrite phase sltifter, where the ferrite slab material 's cross section is increase to 7 x 9 mm, where the cross section of the non-planar structure is 8 x 11 .5 mm. Length of the phase sltifter is 15 cm with a width of7.5 cm.

Figure 8.4 shows the S-paramelers of the proposed ferrite phase shifter when the ferrite

slab material's cross section is increased to 7 x 9 mm. Shown in Figure 8.4 are the return

and the insertion loss at the lower biasing region. As may be seen, the insertion loss

remains low until the ferrite bias reaches 30 kAlm and at this point the insertion loss

makes a significant increase from about -4.3 dB to -17 dB at 40 kAlm bias.

Understanding the physical reasons for such change in the insertion loss which was

observed both in simulation results and the experimental data is yet another topic for

future research.

71

11 .5 nun

9 nun

9mm 2mm

Figure 8.3 Cross section view of future rnicrostrip line-based ferrite phase shifter, where ferrite slab material '5 cross section is increase to 7 x 9 mm

S-parameters for larger ferrite slab cross section

o

-... - ~ -

.~

.,

· ' 0

·15

" -

/ -.JO

"-- "- / -'" 4 0 - S11 larger ferrite ~/

_ S21 larger ferrite

o , ' 0 15 20 2.5 30 " Inllmal Magnetic Bias (kA/m)

Figure 8.4 S-par.meters of future microstrip line-based ferrite phase shifter, where ferrite slab material's cross section is increase to 7 x 9 rnm

72

REFERENCE

[1] F. Reggia and E. G. Spencer, "A new technique in ferrite phase shifting for beam steering in microwave antennas," Proc. IRE. vol. 45, pp.1510-1517, Nov. 1957.

[2] J. D. Adam, L. E. Davis, G. F. Dionne, E. F. Schloemann, and S. N. Stitzer, "Ferrite devices and materials," IEEE Trans. Microwave Theory Tech., vol. 50, pp. 721-736, Mar. 2002

[3] D. M. Pozar, Microwave Engineering, 2nd Ed. New York: Wiley, 1998, chapters 2, 5, 7,&9.

[4] S. K. Koul and B.Bhat, Microwave and millimeter wave phase shifters volume I: Dielectric andferrite phase shifters. MA, Artech House, Inc. 1991

[5] B. R. Norvell, R. J. Hancock, J. K. Smith, M. L. Pugh, S. W. Theis, and J. Kriatkofsky, "Micro electro mechanical switch (MEMS) technology applied to electronically scanned arrays for space based radar," IEEE Aerospace Conference Proceedings, vol. 3, pp. 239-247, 6-13 Mar. 1999.

[6] E. R. Brown, "RF-MEMS switches forreconfigurable integrated circuits," IEEE Trans. Microwave Theory Tech., vol. 46, issue II, pp. 1868-1880, Nov. 1998.

[7] G. Subramanyam, F. A. Miranda, F.V.l Keuls, R.R. Romanofsky, C.L. Canedy, S.Aggarwal, T. V enkatesan, and R. Ramesh, ''Performance of a K-band voltagecontrolled lange coupler using a ferroelectric tunable microstrip configuration," IEEE Microwave and Guided wave letter, vol. 10, no.4, pp 136-138, April 2000.

[8] J. J. Lee and J. V. Strahan, ''Planar ferrite phase shifter," U.S. Patent 5 223 808, Hughes Aircraft Co. (now Raytheon), 29 June 1993.

[9] R. K. Sorensen, M. F. Iskander, and J. J. Lee, "Low-cost nonplanar microstrip line ferrite phase shifter utilizing circular polarization," IEEE Microwave and Wireless Components Letters, vol. 14, issue I, pp. 25-27, Jan. 2004.

[10] R.K. Sorensen, "Novellow-cost nonplanar microstrip line ferrite phase shifter utilizing circular polarization," M.S. thesis, May 2003.

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