Major Proj Repor

8/4/2019 Major Proj Repor

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DESIGN AND SIMULATIONS OF FEEDHORNS FOR SATELITE ANTENNA SYSTEM

A Major Project Report

Submitted in Partial Fulfillment of the Requirements for theDegree of

Bachelor of Technology

IN

ELECTRONICS&COMMUNICATIONENGINEERING

By

Brahmbhatt Soham P. (08BEC153)

Chaudhari Jatin D. (08BEC154)

Under the Guidance of

Prof. Dhaval Pujara

Department of Electrical Engineering

Electronics & Communication Engineering Program

Institute of Technology, Nirma University

Ahmedabad 382 481

May 2011


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CERTIFICATE

This is to certify that the Major Project Report entitled Design and

Simulations of Feed Horns for Satellite Antenna Systems submitted by

Soham Brahmbhatt (Roll No. 08BEC153) & Jatin Chaudhari (Roll No.

08BEC154) as the partial fulfillment of the requirements for the award of the

degree of Bachelor of Technology in Electronics &Communication

Engineering, Institute of Technology, Nirma University is the record of work

carried out by his/her under my supervision and guidance. The work submitted

in our opinion has reached a level required for being accepted for the

examination.

Date:

Project Guide

Prof. Dhaval Pujara

Prof. A. S. Ranade

HOD (Electrical Engineering)

Nirma University, Ahmedabad


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Acknowledgement

We take this opportunity as a privilege to thank all individuals without whose

support and guidance we could not have completed our project in this stipulated

period of time. First and foremost we would like to express our deepest

gratitude to our Project Supervisor Prof. Dhaval Pujara, Department of

Electronic and Communication Engineering. For his invaluable support,

guidance, motivation and encouragement throughout the period of this work.

We are also grateful to Prof.Shailesh Pandey for his valuable suggestions and

inputs during the course of the project work. His readiness for consultation at all

times, his educative comments and inputs, his concern and assistance even with

practical things have been extremely helpful. We would also like to thank all

faculty members of the Department of Electronics and Communication for their

generous help in various ways for completion of the thesis. We also extend our

thanks to our fellow students for their friendly co -operation.


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Abstract

Wireless technology is a one of the main areas of research in the world of

communication systems today and a study of communication systems is

incomplete without understanding of the design and simulation of antenna. This

was the main reason for our selecting a project focusing on this field.

The field of antenna study is an extremely vast one, so, to grasp the fundamental

we dividing our project into different parts.

In the first part we focused on the basic knowledge of the horn antenna and

design method of the pyramidal horn antenna .

Second part we focused on the design and simulations of potter horn in which

the result in complete beam width equalization in all plane complete phase

center coincidence, and at least 30dB side lobe suppression in the electric plane.

Third and the last part we performed simulation on conical horn antenna and

antenna feed system


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Index

Chapter

No.

Title Page

No.

Certificate II

Acknowledgement III

Abstract IV

Index V

List of Figures VII

1. Horn Antenna 8

1.1 Introduction 8

1.2 Background and Theory 8

1.3 Types of Horn Antenna 9

1.3.1 Pyramidal Horn Antenna 9

1.3.2 Sectrol Horn Antenna 10

1.3.3 Conical Horn Antenna 11

1.3.4 Septum Horn Antenna 11

1.3.5 Corrugated Horn Antenna 11

1.3.6 Ridges Horn Antenna 1

2

1.3.7 Aperture Limited Horn Antenna 12

2. Design Method for Pyramidal Horns 13

2.1 Introduction 13

2.2 Design equation of pyramidal horns 13

2.3 Simulation results 15

2.4 Flow chart for Matlab based exercise 16

2.5 Conclusion 16

3. Design and Simulation of Conical Horns 17

3.1 Open-ended rectangular waveguide 17

3.1.1 Field expressions 17


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3.1.2 Simulation results 19

3.2 Open-ended circular waveguide 20

3.2.1 Field expressions 21

3.2.2 Simulation results 22

3.3 Flow chart for Matlab based exercises 23

4. Potter horn 24

4.1 Introduction 24

4.2 Field expressions 25

4.3 Simulation results 27

4.4 Applications 29

4.5 Conclusion 29

5. Antenna feed system 30

5.1 Multimode Cassegrain Monopulse feed 30

5.2 Field expressions 31

5.3 Cross-section of multimode feed 32

5.4 Multimode horn 33

5.5 simulation results 34

6. Conclusion 35

7. References 36


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LIST OF FIGURES

Fig. No. Title Page

No.

1.1 Structure of Pyramidal HornAntenna 10

1.2 Structure of E-Plane Sectrol Horn Antenna 10

1.3 Structure of H-Plane Sectrol Horn Antenna 10

1.4 Structure of Conical Horn Antenna 11

1.5 Structure of Corrugated Horn Antenna 11

2.1 Geometry of Pyramidal HornAntenna 13

3.1 Structure of Open ended Rectangular Waveguide 17

3.2 Radiation Pattern of TE10 Mode for Rectangular Wave Guide 19

3.3 Radiation Pattern of TM10 Mode for Rectangular Wave Guide 20

3.4 Radiation Pattern of TE10 Mode for Circular Wave Guide 22

3.5 Radiation Pattern of TM10 Mode for Circular Wave Guide 22

4.1 Radiation Pattern of TE10 Mode for E-Plane Pattern 27

4.2 Radiation Pattern of TE10 Mode for H-Plane Pattern 27

4.3 Radiation Pattern of TM11 Mode for E-plane Pattern 28

4.4 Radiation Pattern of Dual Mode Conical Horn 28

5.1 Structure of Cassegrain Feed Antenna 30

5.2 Structure of Multimode feed Cross section 32

5.3 Radiation pattern (For A=0.01) of dual mode square waveguide

for TE12 mode in aperture equalizes E-Plane

34

5.4 Radiation pattern (For A=-0.5) of dual mode square waveguide

for TM12 mode in aperture equalizes H-Plane pattern

34


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Chapter 1

Horn Antenna

1.1 Introduction

In todays technological society, wireless communication has become an increasingly

important part of daily life. The antenna is responsible for coupling the RF energy from the

transmission-line feed to free space, and vice versa. Antennas are characterized using several

parameters, such as geometry, gain, beam width, side-lobe level, and frequency of operation,

efficiency, and polarization. The pyramidal horn antenna is part of the aperture antennas

family that has a conical radiation pattern, linearly polarized and it is ideal in high gain

transmission and receiving, peer to peer communications, and as a dish feed.

1.2Background and Theory

Horn antennas are extremely popular in the microwave region above 1 GHz. Horns

provide high gain, low VSWR, relatively wide bandwidth. The horns can be flared

exponentially, too. This provides better matching in a broad frequency band, but is

technologically more difficult and expensive. The rectangular horns are ideally suited for

rectangular waveguide feeders. The horn acts as a gradual transition from waveguide mode to

a free-space mode of the EM wave. The open-ended waveguide will radiate, but not as

effectively as the waveguide terminated by the horn antenna. The wave impedance inside the

waveguide does not match that of the surrounding medium creating mismatch at the open end

of the waveguide. Thus, a portion of the outgoing wave is reflected back into the waveguide.

The horn antenna acts as a matching network, with a gradual transition in the wave

impedance from that of the waveguide to that of the surrounding medium. With a matched

termination, the reflected wave is minimized and the radiated field is maximized.

When radio waves travelling through the waveguide hit the opening, it acts as a

bottleneck, reflecting most of the wave energy back down the guide toward the source, so


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only part of the power is radiated. It acts similarly to an open-circuited transmission line, or

to a boundary between optical mediums with a high and low index of refraction, like a glass

surface. The reflected waves cause standing waves in the waveguide, increasing the VSWR,

wasting energy and possibly overheating the transmitter.

To improve these poor characteristics, the ends of the waveguide are flared out to

form a horn. The taper of the horn changes the impedance gradually along the horn's length.

This acts like an impedance matching transformer, allowing most of the wave energy to

radiate out the end of the horn into space, with minimal reflection. The horn shape that gives

minimum reflected power is an exponential taper. Exponential horns are used in special

applications that require minimum signal loss, such as satellite antennas and radio telescopes.

However conical and pyramidal horns are most widely used, because they have straight sides

and are easier to fabricate.

1.3 Types of Horn Antenna

A horn antenna is an antenna that consists of a flaring metal waveguide shaped like

a horn to direct the radio waves. Horns are widely used as antennas at UHF

and microwave frequencies. Horns can have different flare angles as well as different

expansion curves like elliptic, hyperbolic, in the E-field and H-field directions, making

possible a wide variety of different beam profiles.

1.3.1 Pyramidal Horn Antenna

A horn antenna with the horn in the shape of a four-sided pyramid, with a rectangular

cross section. They are the most widely used type, used with rectangular waveguides, and

radiate linearly polarized radio waves.


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Figure 1.1:Structure of Pyramidal HornAntenna

1.3.2 Sectoral Horn Antenna

A pyramidal horn with only one pair of sides flared and the other pair parallel. It

produces a fan-shaped beam, which is narrow in the plane of the flared sides, but wide in the

plane of the narrow sides.

y E-plane Sectoral Horn AntennaA sectoral horn flared in the direction of the electric or E-field in the waveguide.

Figure 1.2:Structure of E-Plane Sectrol Horn Antenna

y H-plane Sectoral Horn AntennaA sectoral horn flared in the direction of the magnetic or H-field in the

waveguide.

Figure 1.3:Structure of H-Plane Sectrol Horn Antenna


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1.3.3 Conical Horn Antenna

A horn in the shape of a cone, with a circular cross section. They are used with

cylindrical waveguides.

Figure 1.4:Structure of Conical Horn Antenna[1]

1.3.4 Septum Horn Antenna

A horn which is divided into several sub horns by metal partitions (septum) inside,

attached to opposite walls.

1.3.5 Corrugated Horn Antenna

A horn with parallel slots or grooves, small compared with a wavelength, covering the

inside surface of the horn, transverse to the axis. Corrugated horns have wider bandwidth and

smaller side lobes and cross-polarization, and are widely used as feed horns for satellite

dishes and radio telescopes

Figure 1.5:Structure of Corrugated Horn Antenna[1]


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1.3.6 Ridges Horn Antenna

A pyramidal horn with ridges or fins attached to the inside of the horn, extending

down the center of the sides. The fins lower the cutoff frequency, increasing the antenna's

bandwidth.

1.3.7 Aperture Limited Horn Antenna

A long narrow horn long enough so the phase error is a fraction of a wavelength, so it

essentially radiates a plane wave. It has an aperture efficiency of 1.0 so it gives the maximum

gain and minimum beam width for a given aperture size. The gain is not affected by the

length but only limited by diffraction at the aperture. Used as feed horns in radio telescopes

and other high-resolution antennas.


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Chapter 2

Design Method for Pyramidal Horns

2.1 Introduction

A pyramidal horn is the one of the simplest and most reliable microwave antennas. A

simple expression for the narrow aperture dimension of the horn is obtained and used in the

optimum gain pyramidal horn design. The design parameters are computed from the simple

and explicit formulas. These formulas do not need the application of the iterative methods,

and are not restricted to the long-horn designs. The gain of a designed pyramidal horn is

determined without approximating the path length error. An exact solution is presented for

the fourth-order polynomial representing the general horns design problem. When the

available approximations are used for the gain reduction factors, this leads to closed-forms

expression for the aperture, and hence the other, dimensions of the pyramidal horns of any

desired gain and aperture phase error.

2.2 Design Equation for the Pyramidal HornsA Numerical Design method for pyramidal horns for any desired gain and aperture phase

error is describe by selvan ref. [1]

Figure2.1 Geometry of Pyramidal Horn Antenna


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At the point y at the aperture of the horn, the phase of the field will not be same as that at the

origin y=0. The phase is a different because the wave has traveled different distances from

the apex to the aperture.

With the reference to the structure of pyramidal horn antenna with aperture dimension of a

and b1 (b1>a) shown in figure 2.1, the general horn design equation can be written as [2] [4].

. (1)The narrow aperture dimensions of the general pyramidal horn as obtain by solving the

equation (1)

... (3) 4)With

(6) Once b1 is estimated, the other dimensions of the horn can be calculated as follows

The optimum design equations are obtain when one sets s=0.25 and t=0.375


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2.3 Simulation results

Design example y It is required to build an L band horn with following specification

G=15.45dB

F=1GHz

S=0.2

T=0.3

A=24.765cm

B=12.383cm

Numerical result


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2.4Flow chart for Matlab based exercises

2.5 Conclusion

We conclude that for arbitrary gain and aperture phase error, we can design exact

solution for pyramidal horn antenna.

Input Parameter: Frequency, Phase error parameters, Dimension

of the wave uide

Calculate the dimension of horn and gain antenna using the

desi n e uation.

Compare the calculated and theoretical gain

Enter the desired gain which is required to build a horn antenna

START

END


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Chapter 3

Design and Simulation of Conical Horns

3.1 Open-ended rectangular waveguide:

Approximate formulas are derived for the far field and gain of standard, open-ended,

rectangular waveguide probes operating within their recommended usable bandwidth. The

derivation assumes first-order azimuthal dependence for the fields, and an E-plan pattern

given by the traditional Stratton-Chu integration of the transverse electric TE10 mode. The H-

plane pattern is estimated by two different methods. The first method uses purely E-field

integration across the end of the waveguide. The second, more accurate method approximates

the fringe currents at the shorter edges of the guide by isotropically radiating line sources.

The amplitude of the line sources is determined by equating the total measurements indicate

that for X-band and larger waveguide probes, both methods predict on-axis gain to about 0.2

dB accuracy. The second method predicts far-field power patterns to about 2dB accuracy in

the region of 90 deg off bore sight and with rapidly increasing accuracy toward bore sight.

3.1.1 Field expression for open ended rectangular waveguide

Figure 3.1 structure of open ended rectangular wave guide


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The inner dimensions of the waveguide are given by width a and height b. The

perfectly conducting waveguide walls are assumed to have a negligible thickness

compared to the smaller dimension b. The waveguide operates at a frequency f that

lies within the recommended usable bandwidth of the TE10 mode with the electric field

in that direction. the far field of the waveguide expressed as a sum of spherical

multipoles located at the origin. Because the transverse dimensions of t h e waveguide

are less than a wavelength, only the multipoles of lower order azimuthal dependence

will contribute significantly to the far field because all but the first- order multipoles

have a null in the on-axis z- direction, one would expect significant coupling to free

space only from these first-order multipoles. Under this assumption and the symmetry

of the rectangular waveguide excited by the TE10 mode , the far fields of the open-

ended waveguide can be expressed approximately in the following simple form [3]

Where,

=Radian frequency

=permeability =permittivityk=Free space propagation constant

=Polar angle


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=Azimuth angle

R=Distance from the aperture Center to the observation point

The field expression of TM10mode for open ended rectangular wave guide shown below

[3]

).. (4)

..(5)

3.1.2 Simulation results

Figure 3.2 Radiation Pattern (Co-polarization for =0) of TE10 Mode for the

Rectangular wave guide

-80 -60 -40 -20 0 20 40 60 80-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Theta

Eco(dB)

Eco (dB) v/s Theta


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Figure 3.3: Radiation Pattern (Cross-polarization for =0) of TM10 Mode for the

Rectangular wave guide

3.2 Open-ended circular waveguide:

The far field radiation patterns of TEmn-modes and TMmn-modes from open ended

circular multimode waveguides in the E-plane and H-plane are calculated. The possibility and

convenience of identifying the operating mode mixture of high power gyrators with

multimode output and analyzing the mode conversion properties of overmoded waveguide

components by measuring the far field radiation pattern are studied. At certain angles radiated

power is contributed only by one mode from every series of modes with the same m number.

This character is very convenient for mode identification. Mode mixtures in overmoded

waveguides might also be identified by directional couplers, each being prepared for the

selective pick up of a particular mode. Measurements of the voltage traveling wave ratio in

the waveguide by small probes can be related to the composition of the modes inside the

multimode waveguide, but not at high powers.

-80 -60 -40 -20 0 20 40 60 80-300

-280

-260

-240

-220

-200

-180

-160

-140

-120

-100

Theta

E

co(dB

)

Ec o(dB ) v/s Theta


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3.2.1 Field expression for open ended circular waveguide

The far fields of the open-ended waveguide can be expressed for TE10approximately

in the following simple form [3]

.. (7)

The far-fields of the open-ended waveguide can be expressed for TM10 approximately

in the following simple form by [3]

.. (9)


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3.2.2 Simulation results

Figure 3.4: Radiation Pattern (Co-polarization for =0) of TE10 Mode for the

circular wave guide

Figure 3.5: Radiation Pattern (Cross-polarization for =0) of TE10 Mode for the

circular wave guide

-80 -60 -40 -20 0 20 40 60 800

0. 5

1

1. 5

2

2. 5

3

3. 5

4

4. 5

x 10-1 5

Theta

E

co

Eco v /s Theta

-8 0 -6 0 -4 0 -2 0 0 2 0 4 0 6 0 8 00

0 . 1

0 . 2

0 . 3

0 . 4

0 . 5

0 . 6

0 . 7

0 . 8

0 . 9

1

T h e t a

E

co

E c o v / s T h e ta


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3.3 Flow chart for Matlab based exercises

Input Parameter: Frequency, types of mode, mode number,

Permeabilit

Calculate free-space wave number, Cut off frequency

Set range of Theta () and set the value of Phi ().Generally,

=0ofor E-plane pattern and 90

0for H-plane pattern

Enter the general expression of the polar and azimuthal far-field

radiation pattern component of the TE/TM waves.

Calculate the Co and Cross-polarization using Ludwigs third

definition.

Plot the Co-polarization and Cross-polarization radiation

attern.

START

END


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Chapter 4

Potter horn

4.1 IntroductionA conical horn antenna radiating an appropriate mixture of energy in the TE11 and

TM11 modes offers several advantages over a conical horn antenna radiating energy in a

single mode only. Lower side lobe levels with resulting higher directivity, for example, are

achieved with such dual mode radiation. Furthermore, better beam width equalization with

resulting improved circular symmetry is achieved.

A conical horn antenna constructed in accordance with the invention comprises a

tapered circular waveguide having a minimum inside diameter equal to that of a cylindrical

waveguide in which TE11 mode energy can be supported and a maximum inside diameter

equal to that of a cylindrical waveguide in which TE11 and TM11 mode energy can be

supported. Within the tapered waveguide is a circular rod having tapered ends, a dielectric

constant greater than that of air and a length no greater than that of the tapered waveguide.

Several dielectric rings having dielectric constants substantially equal to that of air coaxially

mount the rod completely within the tapered waveguide.

Dual mode radiation is achieved in the prior art through the use of a conical horn

antenna proceeded by a mode converter which converts a portion of energy in the TE 11 mode

into the TM11 mode. For satisfactory dual mode radiation, this TM11 mode energy and the

remaining TE11 mode energy must combine with appropriate amplitudes and phases over the

aperture of the horn antenna. These requirements become a problem, however, because of

two frequency dependent characteristics of the configuration. First, the two modes exist

independently and are no degenerate so that their phase difference over the antenna aperture

depends, for a given horn length, upon the operating frequency. Second, the phase and

amplitude of the mode generated by the converter also depend upon the operating frequency.


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Because of these frequency-dependent characteristics, the widest bandwidth over which the

arrangement performs effectively has been limited to less than 25 percent.

Dual-mode horns are often used as substitutes for corrugated horns which are lossy

and difficult to fabricate for sub millimeter wavelengths. A dual-mode horn with the proper

combination of the circular TE11 and TM 11 modes has a highly symmetrical aperture field

and a relatively low cross polarization level of the total radiated power. Each antenna type

has its advantages and disadvantages. The corrugated conical horn is a popular antenna for

millimeter wavelengths, but they are lossy and difficult to fabricate for sub millimeter wave

lengths.

The idea for the dual-mode horn is thus to excite some amount of the TM11 mode in a

mode converter and then make sure that the two modes have the correct relationship at the

aperture of the conical part of the horn. Since the two modes have different cut-off

frequencies, their dispersion characteristics are different. If some freedom of choice is needed

in terms of horn dimensions, a phasing section is needed to ensure that the proper aperture

field is achieved. All this combined makes the horn rather frequency sensitive, but this is not

so important for some applications.

4.2 Field expressionsy The polar and azimuthal component radiation patterns of TE11mode, are given by

silver Ref. [1]


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Where

=Radian frequency

=permeability

k=Free space propagation constant

a=Aperture half diameter

J1=First order Bessel function of the first kindJ1=First derivative of J1 w.r.t its argument

k11H=First root of J1=1.841=Polar angle

=Azimuth angleR=Distance from the aperture Center to the observation point

y The polar radiation patterns of TE11mode, are given by silver Ref. [1]TM11mode have no azimuthal electric field component in any direction Ref. [1]

. (4)Where,

k11E=First root of J1=3.832

y In order the calculate the performance of the dual mode conical horn in the electricplane equation (1) and (3) may be simplified and combined as follow.


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4.3 Simulation Results

Figure 4.1 Radiation pattern (Co-polarization for =0) of TE11 mode for E-plane

Pattern

Figure 4.2 Radiation pattern (Co-polarization for =0) for of TE11 mode for H-plane

Pattern

-80 -60 -40 -20 0 20 40 60 80-6 0

-5 0

-4 0

-3 0

-2 0

-1 0

0

Theta(Deg)

E

co(dB

)

H p l a n e P a t te r n

-80 -60 -40 -20 0 20 40 60 80-60

-50

-40

-30

-20

-10

0

Theta(Deg)

Eco(dB)

E plane Pattern


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Figure 4.3 Radiation pattern (Co-polarization for =0) of TM11 mode for E-

plane

Pattern

Figure 4.4 Radiation pattern (Co-polarization for =0) of Dual Mode Conical Horn

-80 -60 -40 -20 0 20 40 60 80-60

-50

-40

-30

-20

-10

0

Theta(Deg)

E

co(dB

)

E p l a n e P a t te r n

-80 -60 -40 -20 0 20 40 60 80-6 0

-5 0

-4 0

-3 0

-2 0

-1 0

0

Theta(Deg)

E

co(dB

)

E p la n e P a tte rn


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4.4 Applications

The dual mode conical horn has less axial gain than a dominant mode conical horn

with the same aperture size .Its also used for gain standards, anechoic chamber illuminators,

and pattern range illuminators. One of the most important applications for the dual-mode

conical horn is Cassegrain feed systems.

4.5 Conclusion

Anew type of conical-horn antenna has been described in which both the dominant

TE11 mode and the TM11 mode are utilized to effect beam width equalization, phase center

coincidence, and almost complete side lobe suppression.


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Chapter 5

Antenna feed system

5.1 Multimode Cassegrain Monopulse Feed

Figure 5.1 structure of Multimode Cassegrain Monopulse Feed

Cassegrain antennas are widely used in todays world of millimeter wave

communications. Due to the high gain and pencil-sharp beam width they are mostly used for

point-to-point links and mesh network terminals, but also works well for radar and satellite

communication applications. The fact of Cassegrain antennas popularity is based on a general

rule, that if the diameter of the main reflector is greater than 100 wavelengths, the Cassegrain

system is a contending option compare to other antenna types.

The Cassegrain design employs a parabolic contour for the main dish and a

hyperbolic contour for the sub dish. One of the two focuses of the hyperbola is the real focal

points of the system and is located at the center of the feed; the other is a virtual focal point

which is located at the focus of the parabola. The main advantages of Cassegrain antenna are

a reduction in the axial dimensions of the antenna just as in optics and a greater flexibility in

the design of the feed system.

The main reflector is most expensive part of the of Cassegrain antenna and usually

made from a metal-coated composite plastic or machined from a chunk of metal. Plastic


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reflectors are cheaper but are subjected to hogging under direct sunlight and curling of

coating at the regions with a wet climate. The other problem associated with plastic reflectors

is a technology processing complexity to make an ideal fidelity hyperbola with a micron

tolerance for high frequencies from a plastic material. Thats why steel or aluminum dishes

are used to design Cassegrain antennas for serious commercial products on broadband

communications market.

Features

y Low VSWRy Aluminum or Fiberglass Constructiony Low Loss Performance at Millimeter Frequenciesy Available from 2Ghz to 140Ghz

Applications

y Radar and Satellite Trackingy Communication Systems

5.2 Field expressions

The suppressed side lobe feed consists of a conical horn using the TE 11 mode for the

basic radiation pattern, and adds the TM11 mode for the side lobe suppression in the E-

Plane. Field expression for TE11 and TM11 modes are given by [3]

= E-plane .. (1)

=0 H-plane (2)


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A combination of the TE12 and TM12 modes for the E-Plane suppression and fieldexpression is given by [3]

= E-plane. (3) ..(4)TE30 mode is used for H-Plane suppression and the field expression is given by[3]

= E-plane . (5) =0 H-plane (6)The additional modes necessary are the TE10 for H-plane monopulse, and the TE11 and

TM11 mode combination for E-plane monopulse.

5.3 Cross-section of multimode feed

Figure 5.2 Cross section of multimode feed

The Monopulse Bridge feeding the common aperture section is a standard four

guide monopulse circuit providing dual polarization capability.

The matching section provides a match for all modes from the bridge input to

the multimode horn. Along with the basic modes desired, additional higher order

modes are excited to meet the boundary conditions. These modes are below cutoff in

the matching section, thus causing a large reactive mismatch which must be

compensated for by the matching section.


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The difference mode phasing section is required to ensure the proper phasing

between the TE10 and the composite TE11+TM11 mode. This is necessary because of

the difference in propagation velocity between the modes through the length of the

horn. The length of this section is chosen to provide the additional differential phase

shift between the modes to result in the correct phase relation at the aperture.

The sum mode excitation and control section is the most critical portion of the

horn. The step between region C and D is chosen such that in addition to the TE10

mode, the TE12+TM12 and TE30 modes are excited from the incident TE10 mode with

the correct amplitude. The field configurations of these modes were shown in figure.

The size of this section a must be large enough to support all modes up to the TE30

mode. However, it must not permit propagation of any higher modes excited by the

incident TE13+TM13 mode combination from TE11+ TM 11 incident modes. Therefore,

the dimension must be chosen above cut-off for the TE30 mode and below cut-off for

the TE13 mode.

The design of this horn section requires consideration of both the aperture phase

error and phasing between the sum patterns modes. The flare angle should be such that

the phase error across the aperture is not excessive as in any horn design.

5.4 Multimode horn

For many applications the single-mode horn is not satisfactory, especially the

rather high side lobe and the difference between E-plane and H-plane patterns. Seen

from an aperture-theory point of view the obvious solution is to modify the aperture

illumination in such a manner that the desired properties are obtained. In doing this it

is customary to neglect the sphericity of the horn modes and discuss the corresponding

waveguide only, where the waveguide cross-section.


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5.5 Simulations:

Figure 5.3 Radiation pattern (For A=0.01) of dual mode square waveguide for

TE12 mode in aperture equalizes E-Plane

Figure 5.4 Radiation pattern (For A=-0.5) of dual mode square waveguide for

TM12 mode in aperture equalizes H-Plane pattern

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0-5 0

-4 5

-4 0

-3 5

-3 0

-2 5

-2 0

-1 5

-1 0

-5

0

Theta(Deg)

E

co(dB

)

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0-5 0

-4 5

-4 0

-3 5

-3 0

-2 5

-2 0

-1 5

-1 0

- 5

0

T h e ta (D e g )

E

c

o

(d

B

)


35/36

35

Conclusion:-

We have given detail explanation of our project. We finally concluded that our

project is completed in given time limit with satisfaction. while doing this project we

learn about various engineering fields helps each other to make different kind of work

easily. We visited various workshops, and engineering shop, which is required. We learn the

group work from this project , which is important for our future industrial life & how to

manage with different skilled persons & how to work in different conditions without

losing more time how we can give our best work to our project industrial life, As part

of this interface.


36/36

References:

[1.]Constantine A. Balanis, Antenna Theory Analysis and Design, Second Edition.[2.]K. T. Selvan, Accurate design method for optimum gain pyramidal horns, Electron.

Lett vol. 35, no. 4, pp. 249-250, Feb. 1999, [Corrections, Electron. Lett. Vol. 35, no.7, p. 607, Apr. 1999].

[3.]Silver S., Microwave Antenna Theory and Design, McGraw-Hill Book Company,lnc. New York, 1949, Chapter 10.

[4.]J. F. Aurand, Pyramidal horns, part 2: Anovel design method for horns of anydesired gain and aperture phase error, in Proc. IEEE Antennas Propag. Symp, Jun.

1989, vol. 3, pp. 14391442.

[5.]Jensen. P. A., Low Noise Single Aperture Cassegrain Monopulse Feed, inventionDisclosure PD 5462, Hughes Aircraft Co.

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