A NOVEL RESONANT MICROSTRIP RF PHASE SHIFTERUSING DEFECTED GROUND STRUCTURE

Jun-Seok Park, Chul-Soo Kim, Hyun Taek Kang*, Geun-Young Kim**, Kyu-Ho Park***, and Dal AhnDept. of Electronics, Soonchunhyang Univ. Chungnam, R.O.Korea

*Ace Technology Inc., R.O.Korea**School of Engineering, Tamna Univ., R.O.Korea

***Korea Electronics Technology Institute, Telecommunication Components Research center, R.O.KoreaE-mail: ahnramrec.sch.ac.r

Abstract - In this paper, novel RF phase shifterstructure using DGS (Defected Ground Structure) isproposed for the low insertion loss and linear phasevariation characteristic. Equivalent circuit of theproposed phase shifter is derived by employing theequivalent circuit of DGS section. Varactor diode ischosen as an electrical control device, which is placedon metallic backside ground plane. Theoreticalconsideration and experiments verify the presentedphase shifter. The experimental results for a single-stage resonant phase shifter show a range of 25°- phasevariation with 0.5dB insertion loss within an operatingbandwidth of 10%, when the center frequency is900MHz.

I. INTRODUCTION

Several possible designs for adjustable phase shifterssuch as switched line type, reflection, and load line havebeen developed. [1], [2], [3] Recently, electricallyadjustable phase shifters with bits control, which havenumber of phase varying sections in order to provide widerange of phase variation, have been reported at microwaveand millimeter frequency bands with variousconfigurations such as MEMS and MMICs. Electricallyadjustable phase shifters are usually built with varactordiodes when a continuous phase adjustment is required.However, the phase shift of available varactors becomesquite limited due to chip and package parasitics.Furthermore, varactors have poor unloaded Qcharacteristic depended on operating frequency range sothat a phase shifter has poor insertion loss characteristic. [4]

In this paper, novel resonant microstrip RF phaseshifter using DGS is proposed for the low insertion lossand linear phase variation characteristic. Proposed phaseshifter is intended to decrease effects of parasitics and poorQ of varactor by placing the varactor on metallic groundplane. Equivalent circuit of the proposed phase shifter isderived by employing the equivalent circuit of DGS

section. [5] In order to show validity of the proposed phaseshifter, theoretical consideration and experiments arecarried out. The experimental results show a range of 25°-phase variation with excellent insertion loss characteristicwithin an operating bandwidth of 10%.

II. EQUIVALENT CIRCUIT OF THE PROPOSEDPHASE SHIFTER

Fig.1 shows the proposed resonant microstrip phaseshifter configuration. The DSG section, which is etched onthe ground metallic plane, was chosen as a resonator. Inorder to show the principle of operation of single-stageresonant phase shifter, the equivalent circuit of theproposed phase shifter should be derived. Fig.2 showsconfiguration of DGS, which is for realization of theresonant microstrip phase shifter. The equivalent circuit ofproposed phase shifter depends on that of the DGS. TheDGS sections can be replaced with parallel LC resonators.The equivalent circuit and extraction method of circuitparameters for DGS is detailed in [5]. Thus, the equivalentcircuit of proposed single-stage resonant phase shifterbecomes adjustable parallel LC resonator withtransmission lines as shown in Fig.3.

Varactordiode

Microstrip /l ine /

/ Ai--=--===i --------=---=-Etched DGS/

on ground plane//I

ground pl

apacit

Fig. 1 Proposed resonant microstrip phase shifterusing DGS.

0 t'lan{ l jZ, _Z sec2 1 +I Z, + Z )cot(2/3l+r)}

(4)where, r =tan-1(2ZBr)

w

(a) (0)Fig.2 DGS for realization of the resonant microstrip phase

shifter. (a) Top view (b) bottom view. The distance gand gi is 0.5mm and 1.5mm. The lattice dimensionis a=10.5mm,h= 7.7mm, and W1=5mm. Conductorwidth Wis 1.2mm.

Fig.3 Detailed equivalent circuit of proposed adjustableresonant phase shifter using DGS.

To show the principle of operation of single-stage resonantphase shifter, we derive the ABCD parameters ofequivalent circuit seen in Fig.3 as follow

[os I jZ, sin, I1 [ 1jI FCos/3I jZisin/311

1,(1)

A D sin in2/1 S P

A=D= cos2p/+2 sin,B1co2/1 ZiBr

B= {Zlsin23l- Cos2/}

III. SIMULATIONS AND EXPERIMENTS

In order to show the validity of the proposed-resonantmicrostrip phase shifter structure, we designed phaseshifter at the center frequency of 900GHz with single LCparallel resonator, which is realized by DGS. Bandwidthand was chosen to be 10%. Dimensions of DGS forrealization of the resonant microstrip phase shifter wereshown in Fig.2. To simulate the proposed resonant phaseshifter with its equivalent circuit, we extracted theequivalent circuit parameter of DGS section for givendimensions. [5] The extracted inductance and capacitancefor given dimensions are 3.5nH were 0. 107pF,respectively. Fig.4 and Fig.5 show simulation results byusing Ansoft Serenade 8.0. Simulation was carried out byreplacing the varactor with its equivalent capacitances fordifferent control voltages. The characteristic impedance oftransmission line was chosen to be 50 ohm for goodmatched characteristic. Simulation results show a range of250-phase variation with good loss characteristic within anoperating bandwidth of 10%. In order to archive largerphase shift characteristic with low insertion loss, severalresonator sections, which are realized by using DGSsections, should be employed as a multistage resonantmicrostrip phase shifter. However, a multistage resonantphase shifter has an additional mismatched loss due tochanging the characteristic impedance of transmission linewhile adjusting the phase shift. [4]

(2)

c.{sin2p/3 sin2f /}C= I t ZI + Z2:

Using derived ABCD parameters and following relationbetween S-parameter and ABCD parameters, we can

derive the phase of transmitted signals. Thus, as the circuitis tuned around its resonant frequency, the introducedphase shift is changed. If an amplitude variation is allowed,wide range of a phase shift variation can be expected.

S212

BA+ +CZ +D

zo

-2ED

go : X6 90DI 920 m ff

Frequency[.MHZI

Fig.4 Simulation results with control capacitance of 29.5pF.(3)

0of S21

0 0. 0 0 0

i

-Mag ftdeoISg dudo 21

I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1D ...... .......

requency~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... pM1Fig.5 Siulation esults ith contol capaitance o 6pFP(b

-12 0000000000000000.i,~~~~~,Fi.6Mesuemntreuls.it.basof0.ols

varacto diodeatfor reaultwizti onthesiultcapacitanceo p b

3OpF with no bias and capacitance6ofsureent6pFltwithbiasobiasolof1voTs, respgetsively.Te-spaerfsormance fcrfabricpated()Sprmtr bPaecaatrsi

paeshifterwaabreishown ind Fige6 manduFigd. Phstaseshftoa

Furthermore,ntha fabricatedtphae sif0TehAsCaNICex icln

loss characteristicnsand ophas shifth as fnthionsCofsethe' 33

va00MHz aroeshown rainaFig.8 theoverallphaseshiftcithinc

rang of0V29To1vOlS.HThe phas shift rang canabetanrther

is increase to 4bia with icreasitngcte ontrol volthbags.o

both cases shows good agreemenFig7tMeaurementresutsuwihtbiasofe11volts

loss characteristic and phaseshi()fS-paametess(b)nhaseoharactristi

(a)

0

-2

-4

-6

-8

-10

-12

-14

-16

-18

-20

-22

-24

-90

-92

-94

-96

-98

-100

-102

-104

-106

-108

-110

IV. CONCLUSION

.

*. _I

0 1 2 3 4 5 6

Vcc [ volt]

(a)

7 8 9 10

In order to realize linear phase shift with low insertionI loss characteristic, the resonant microstrip phase shifter

with DGS section was newly proposed. The equivalentcircuit of the proposed phase shifter was derived based onthe derived equivalent circuit of DGS. The experimentaldata show clearly the excellent insertion loss and phaseshift characteristics. To obtain larger phase shifts severalDGS sections as a resonator with varactors can beconcatenated into a multistage resonant phase shifter. Themeasurement on the fabricated phase shifter shows validityof the proposed configuration and its equivalent circuitrepresentation. The newly proposed resonant type phaseshifter can be expected to adapt to MCM or MMICapplication.

REFERENCES

0 1 2 3 4 5 6 7 8 9 10 11

Vcc [ volt ]

(b)

Fig.8 Measurement results (a) S-parameters vs. controlvoltage (b) Phase characteristic vs. control voltage.

[1] W. A. Little, J. Yuan, and C. C. Snellings, "Hybridintergarted circuit digital phase shifters," IEEE Int.Solid-state Circuit Conf Dig., pp.58-59, 1967.

[2] B. W. Battershall and S. P. Emmons,"Optimization of diode structures for monolithicintegrated circuits," IEEE Trans. MicrowaveTheory Tech., Vol. MTT-16, pp.445-450, July1968.

[3] J. F. White, "High power, p-i-n diode controlled,microwave transmission phase shifters," IEEETrans. Microwave Theory Tech., Vol. MTT- 13,pp.233-242, Mar. 1965.

[4] M. Vidmar, "Microstrip resonant phase shifter,"Microwave Journal, Vol.42, No.9, pp.127-136,Sep. 1999.

[5] J. I. Park, C. S. Kim, J. S. Park, Y. Qian, D. Ahn,and T. Itoh, " Modeling of photonic bandgap andits application for the low-pass filter design,"APMC'99 Dig., pp.331-334, Dec. 1999.

D)

Fig.9 Photograph of the fabricated phase shifter(a) Top view (b) bottom view

m

Ea-

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a)

a1)

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