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HFSS SIMULATION OF NEAR-FIELD BEAM FORMING USING S-BANDRECTANGULAR HORN ANTENNA ARRAY FOR HYPERTHERMIA THERAPY

APPLICATIONS

Dhara Kiritkumar Trivedi

B.E, Gujarat University, India, 2006

Thomas D Jerome-SurendranB.E, Anna University, India, 2005

PROJECT

Submitted in partial satisfaction of the requirements for the degree of

MASTER OF SCIENCE

in

ELECTRICAL AND ELECTRONIC ENGINEERING

at

CALIFORNIA STATE UNIVERSITY, SACRAMENTO

FALL

2009



HFSS SIMULATION OF NEAR-FIELD BEAM FORMING USING S-BAND

RECTANGULAR HORN ANTENNA ARRAY FOR HYPERTHERMIA THERAPY

APPLICATIONS

A Project

by

Dhara Kiritkumar Trivedi

Thomas D Jerome-Surendran

Approved by:

__________________________________, Committee Chair

Dr.Preetham B. Kumar

__________________________________, Second Reader

Dr.Jing Pang

___________________________ Date

ii



Students: Dhara Kiritkumar Trivedi

Thomas D Jerome-Surendran

I certify that these students have met the requirements for format contained in the

University format manual, and that this project is suitable for shelving in the Library and

credit is to be awarded for the Project.

___________________, Graduate Coordinator ____________

Dr.Preetham B. Kumar Date

Department of Electrical and Electronic Engineering

iii



Abstract

of

HFSS SIMULATION OF NEAR-FIELD BEAM FORMING USING S-BANDRECTANGULAR HORN ANTENNA ARRAY FOR HYPERTHERMIA THERAPY

APPLICATIONS

by

Dhara Kiritkumar Trivedi and Thomas D Jerome-Surendran

The focus of this project is to carry out an accurate simulation study of a 3- element array

of rectangle horn antennas forming a focused near field beam. This study has useful

application for clinical hyperthermia which is the therapeutic treatment of tumors in the

body by heating caused by focused RF or microwave radiation. This principle of

treatment is proved to be very useful for cancer treatment usually in conjunction with

traditional radiation or chemotherapy, and can even double the tumor response rate as

compared to radiation alone.. The 3-element array set up consists of a central focusing

element and two surrounding directing elements. The focusing element can be axially

adjusted and surrounding elements are fixed to focus the beam of a required point, which

is necessary in hyperthermia treatment. In this project the simulation results were

obtained from ANSOFT HFSS simulations.

, Committee Chair

Dr.Preetham B. Kumar

______________________

Date

iv



ACKNOWLEDGEMENT

Man has made language to express his feelings. Yet, we find ourselves short of words

when it comes to thanking all those who have rendered necessary help for the completion

of this project.

First and foremost we would like to express our gratitude and thanks to our advisor,

committee chair and graduate coordinator Dr. Preetham Kumar for his expert guidance

and constant support throughout this project. His openness and enthusiasm have taught us

correct way of working with new technologies and have improved our knowledge of the

subject. Also, his constant vigilance with the right amount of freedom, not only as a

project guide but as a guardian too.

We are extremely thankful to Dr. Jing Pang, our second reader, for reviewing this work

and for her valuable suggestions in improving the same. It is our duty to recognize the

efforts of Electrical Engineering Department and the management for creating an

interactive atmosphere for learning.

We would also like to take this opportunity to thank the considerate faculty and staff of

Electrical and Electronics Engineering Department who have been encouraging us

through out our curriculum.

v



At the end we would like to extend our thanks to our parents for their constant

encouragement and to all those who have played a small but important role in this project

but could not be individually named here.

TABLE OF CONTENTS

Page

Acknowledgement………………………………………………………………………..v

List of Tables…………………………………………………………………………….vii

List of Figures……………………………………………………………………...…...viii

Chapter

1. INTRODUCTION..........................................................................................................1

2. ANSOFT HIGH FREQUENCY STRUCTURE SIMULATOR....................................32.1 Introduction to HFSS.................................................................................................3

2.2 Theory behind HFSS High Freuency Structure Simulator……………..…...……...4

2.3 Finite Element Method (FEM) Software…………..………………..……………...42.4 FEM Problem Constraints………………………………………………………….5

2.5 Ansoft HFSS Project Flow..………………………………………………………..52.6 Configuration and Accessing Project Manager………………………………….....62.8 Command and Display Area………………………………………………………..8

2.9 Steps for drawing geometric model.........................................................................10

3. INFORMATION ABOUT HYPERTHERMIA............................................................143.1 Causes of Hyperthermia..........................................................................................14

3.2 Meaning of Hyperthermia........................................................................................14

3.3 Methodology for Hyperthermia Treatment.............................................................153.4 Types of Hyperthermia……………….……………..………………………….…15

3.5 Types of Hyperthermia Treatment…………………………..…………………….17

3.6 Side effects of Hyperthermia………...……………………………………………183.7 Future scope for Hyperthermia …………………………………………………...18

4. DESIGN AND SET UP OF S BAND RECTANGULAR HORN ARRAY.................19

4.1 Measurement of near-field of single horn Antenna along the axis of the antenna...204.2 Measurement of Z axis near-field of 3element horn antenna array..........................21

4.3 Experimental Characterization of current distribution in the feed network……..…….25

vi



5. SIMULATION RESULTS OF S BAND RECTANGULAR HORN ARRAY……....26

5.1 HFSS setup, simulation and array parameters……….…………………………….26

5.2 HFSS simulation with new parameter…………...……………………...…………34

6. CONCLUSION AND SCOPE FOR FUTURE WORK................................................40

References..........................................................................................................................41

LIST OF TABLES

1. Table 5.1 Comparison of Measured and Simulated data……………………………38

vii



LIST OF FIGURES

1. Figure 2.1 Ansoft HFSS Project Manager………......................…………………….....7

2. Figure 2.2 Command Window…….. …………….………………………….……......8

3. Figure 2.3 Flow Chart for simulation in Ansoft HFSS………….…………...…..........9

4. Figure 2.4 3D Modeler Window…………………………………………….……..... 10

5. Figure 2.5 3D View of Geometric Model……………………..……...………..……. 11

6. Figure 2.6 3D view of HFSS solution setup window.....………………....…………. 12

7. Figure 2.7 E and H Field Pattern in HFSS..……………....…………………………. 12

8. Figure 2.8 Post progressing far field…………………………...………………..….. 13

9. Figure 4.1 Photograph of 3 element horn array set up in lab…………………….…..19

10. Figure 4.2 Experimental setup for single-element antenna…..…………….;………20

11. Figure 4.3 Axial near zone electric field of single horn antenna………..…………...21

12. Figure 4.4 Experimental setup for 3-element horn array with 3 elements in line.......22

13. Figure 4.5 Experimental setup for 3-element horn array with central element 5.08 cm behind outer directing elements……………………………………………………...23

14. Figure 4.6 Experimental setup for 3-element horn array with central element 10.16cm

behind outer directing elements…………………………………………………..….24

15. Figure 4.7 Consolidated beam focusing demonstration for 3-element horn array .....25

16. Figure 5.1a HFSS Schematic when all elements are in line………………...…….…27

17. Figure 5.1b Electric field along a XY plane at the highest field point………….…...28

viii



18. Figure 5.1c Near Field pattern (actual distance= 30 cm) all horn antennas are inline…............................................................................................................................28

19. Figure 5.2a HFSS schematic when all elements are in line……………….……..…..29

20. Figure 5.2b Electric field along a XY plane at the highest field point…….…..….....30

21. Figure 5.2c Near field pattern (actual distance = 30 cm) center element is 5 cm behind

the other two elements………………………………………………………...……..31

22. Figure 5.3a HFSS schematic when all elements are in line………………………....32

23. Figure 5.3b Electric field along a XY plane at the highest field point…….………..33

24. Figure 5.3c Near field pattern (actual distance = 30 cm) center element is 10 cmbehind the other two elements…………………………………………………….....34

25. Figure 5.4a Near field pattern (actual distance = 30 cm) all elements are in line.…..35

26. Figure 5.4b Near field pattern (actual distance = 30 cm) center element is 5cm behindthe other two elements……………………………………………………………….36

27. Figure 5.4c Near field pattern (actual distance = 30 cm) center element is 10 cm

behind the other two elements…………………………………………………….....37

ix



Chapter 1

INTRODUCTION

Microwaves are short electromagnetic waves with short wavelength. A credible

definition comes from Pozar's text "Microwave Engineering" [10], which states that the

term microwave "refers to alternating current signals with frequencies between 300 MHz

(3 x 108 Hz) and 300 GHz (3 x 1011 Hz). However, the boundaries between far infrared

light, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used

variously between different fields of study. Due to its unique characteristics microwave

components are used in a variety of applications in today’s world. From communications

to imaging, remote sensing, heating methods, microwaves have been used in a variety of

ways to suit the ever growing demands of the industry. Along with such widespread

applications, microwaves are also used in certain niche applications. One such

application is the use of microwaves for medical diagnostic and treatment. This area of

research has been quietly gathering pace and has been moving slowly but steadily

towards solving the growing needs of medical science.

The microwave electric field has two main components associated with it: the first

one, known as Far Field, is used in communication systems. The second component,

known as Near Field, has applications primarily targeting the medical imaging & therapy

techniques.

Microwave Hyperthermia is a very important near field component of

Electromagnetic energy, and the S-band frequency range of 2.45 GHz is found to be very

1



suitable for heat absorption [1]. Hyperthermia is a form of treatment given to cure the

tumors in different parts of body. The tumor area is heated to therapeutic temperatures of

about 42°C, without over-heating the surrounding normal tissues. Special care and

intense sharp beam focus is required in order to avoid the heat radiation in surrounding of

the tumor. This is the point where accurate antenna setup and formation of conformal

microwave antenna radiation is required.

The aim of this project is the theoretical study of a 3-element array of rectangular

horn antennas, operating in the S-band frequency range of 2.45 GHz. The aim of the

array is to obtain a beam focus at a prescribed point in the near field of the array. The

array also has the ability to move the focus point along the axial direction of the array by

adjusting the position of the central focusing element of the array. The theoretical

simulations are done using Ansoft High Frequency Structure Simulator (HFSS).

The report is organized as follows: Chapter 1 is an introduction. Chapter 2

describes the Ansoft HFSS software. Chapter 3 explains background on clinical

hyperthermia. Chapter 4 gives details of the three-element array simulation for different

focusing points along the axis of the array. Chapter 5 gives conclusions from the results

obtained and direction for future work, followed with the references.

2



Chapter 2

ANSOFT HIGH FREQUENCY STRUCTURE SIMULATOR

2.1 Introduction to HFSS

Ansoft High Frequency Structure Simulator (HFSS) is interactive software that

allows you to characterize full wave and radioactive effects for passive high frequency

transmission structures. Using finite element based solvers. We used Ansoft HFSS ver.

11 which is allows you to compute and view the following:

• Basic Electromagnetic Field quantities, antenna parameters, and for open

boundary problems, radiated fields.

• characteristic port impedance and propagation constants

• Generalized S-parameters and S-parameters renormalized to specific port

impedances.

You are expected to draw the structure, specify material characteristic for each

object and identify ports, sources and special surface characteristics. The system then

generates the necessary field solutions. As you setup the problem HFSS allows you to

specify whether to solve the problem at one specific frequency or at several frequencies

within a range.

Ansoft HFSS ver. 11 is available on UNIX workstations running X windows and

personal computers running Windows NT. The version available at CSU Sacramento is

available on Windows. In HFSS, the geometric model is automatically divided into a

large number of tetrahedral, where a single tetrahedron is basically a four-sided pyramid.

The collection of tetrahedral is referred to as the finite element mesh.

3



Dividing a structure into thousands of smaller regions (elements) allows the

system to compute the field solution separately in each element. The smaller the system

makes the element, the more accurate the final solution will be.

Solving the Maxwell’s equations for every tetrahedron and thereby forming the

wave equations bring about the solution of the structure. The wave equations are then

solved considering the medium of propagation, material properties, the input output ports,

modes, number of solution points and the frequency range selected.

The next section describes the various steps to be followed in order to develop the

structure, bring about the solution and analyze the same for any given structure.

To access Ansoft HFSS, you must first access the Maxwell control panel which

allows you to create and open projects for all projects.

2.2 Theory behind HFSS High Frequency Structure Simulator

• Uses Finite Element Method (FEM) to solve EM problems

• Frequency Domain Solution

• Full wave Solver

• Different Methods of Electromagnetic Analysis

2.3 Finite Element Method (FEM) Software

FEM software is a design tool for engineers and physicists, utilizing rapid

computations to solve large problems insoluble by analytical, closed-form expressions.

4



The “Finite Element Method” involves subdividing a large problem into

individually simple constituent units which are each soluble via direct analytical methods,

then reassembling the solution for the entire problem space as a matrix of simultaneous

equations .FEM software can solve mechanical (stress, strain, vibration), aerodynamic or

fluid flow, thermal, or electromagnetic problems.

2.4 FEM Problem Constraints • Geometry can be arbitrary and 3-dimensional

• Model ‘subdivision’ is generally accomplished by use of tetrahedral or hexahedral

(brick) elements which are defined to fill any arbitrary 3D volume

• Boundary Conditions (internal and external) can be varied to account for different

characteristics, symmetry planes, etc.

• Size constraints are predominantly set by available memory and disk space for

storage and solution of the problem matrix

• Solution is created in the frequency domain, assuming steady-state behavior

2.5 Ansoft HFSS Project Flow

• Configuration

• Drawing

• Boundary

• Source

• Excitation

• Solution

5



• Setup

•

Solving

• Analyze

• Data

• Plot

2.6 Configuration and Accessing the Project Manager:

To configure HFSS 11 following steps should be followed.

Click HFSS 11 to start the problem

Click: File Save As filename

Click: Project Insert HFSS design

Now, HFSS design interface has 6 sub-windows: project window, property window,

drawing window, history window, message window and execution window.

1) On Windows machine Open Ansoft HFSS.

2) Click the left mouse button on the Projects button in the Maxwell control panel to

access the Project Manager.

The project manager window appears as follows

6



Figure 2.1: Ansoft HFSS Project Manager

The directory path that appears at the top of menu points to the default directory

that you specified when you installed the software, which may not necessarily be your

current directory. We can create a new project directory and store the projects in it.

The executive commands window acts as a doorway to each step of creating and solving

the model problem. You select each module through the executive commands menu and

software brings you back to this window when you are finished. You also view the

solution process through this window. The executive commands window is divided into 2

sections:

1) The commands area.

2) The display area

7



8



Figure 2.2: Command Window

2.8 Command and Display Area:

The commands area located on the left side of the screen contains the menu that

let’s you define the type of problem you are solving and then call up the various modules.

The display area shows the project’s geometric model. The following flowchart depicts

the chronological order of events to solve and simulate the structure using Ansoft HFSS

ver. 11.

9



Figure 2.3: Flow Chart for simulation in Ansoft HFSS

10



11



Figure 2.4: 3D Modeler Window

2.9 Steps for drawing geometric model

1) Draw geometric model:

To draw the geometric model, use the solid modeler which is the portion of

Ansoft HFSS that allows you to create objects.

Choose draw from the executive commands menu. The solid modeler appears as shown

in figure 5.By default the draw screen provides you with four views into the problem

region.

a) Three Windows are 2-dimensional, depicting the XY, YZ and XZ axis.

b) The other Window is a 3-dimensional window.

When creating an object any of the windows, the corresponding ports would also be

created in the other three windows.

12



Figure 2.5: 3D View of Geometric Model

3) Solution Set up Assign material properties:

To completely set up the structure, you must assign material characteristic to each

object even those that merely represent the location of boundary conditions and ports in

the geometric model. To set material properties for the objects:

To display the define material menu

a) Choose set up materials. The defined material menu appears as shown in

Figure2.6.

Figure 2.6: 3D view of HFSS solution setup window

13



Figure 2.7: E and H Field Pattern in HFSS

Figure 2.8: Post progressing far field

14



15



Chapter 3

INFORMATION ABOUT HYPERTHERMIA

Hyperthermia is overheating of the body. The word is made up of "hyper" (high) and

"thermia" from the Greek word "thermes" (heat). [3]

3.1 Causes of Hyperthermia

Based on these different parameters, Microwave is more dominant in therapeutic

applications in tissue heating. Among all developed methods this is most promising in

the hyperthermia treatment of cancer, and also does not have any side effects and

produces a minimum discomfort for the patient. By generating very narrow beam it is

possible to heat affected tumors of the part of body and protect healthy tissues.

3.2 Meaning of Hyperthermia

Hyperthermia is a heat cancer treatment applied locally to tumors, raising tumor

temperature to about 42.5ºC (108ºF) for about 45 to 60 minutes. Heat improves blood

circulation and makes tumor cells more susceptible to radiation therapy, killing them

more efficiently and quickly. Hyperthermia can be compared with an artificial fever that

attacks cancer cells. The combination of both, hyperthermia and low dose radiation

makes this therapy the most efficient cancer treatment available today. [4]

In local hyperthermia, heat is applied to a small area, such as a tumor, using

various techniques that deliver energy to heat the tumor. Different types of energy may

be used to apply heat, including microwave, radiofrequency, and ultrasound. [6]

In another approach, called perfusion, the patient's blood is removed, heated, and

then pumped into the region that is to be heated internally. Whole-body heating is used to

16



treat metastatic cancer that has spread throughout the body. It can be accomplished using

warm-water blankets, hot wax, inductive coils (like those in electric blankets), or thermal

chambers (like incubators).

A number of challenges must be overcome before hyperthermia can be considered

a standard treatment for cancer. Many clinical trials are being conducted to evaluate the

effectiveness of hyperthermia. Some trials continue to research hyperthermia in

combination with other therapies for the treatment of different cancers. Other studies

focus on improving hyperthermia techniques. [6] Suggests strongly that, when

hyperthermia is used in combination with radiation therapy or chemotherapy, an

improvement in response rates can be achieved. Hyperthermia can be helpful with

palliation, often dramatically reducing pain.

3.3 Methodology for Hyperthermia Treatment [6]

Usually, other forms of cancer therapy such as radiation therapy and

chemotherapy are used in combination with hyperthermia. Hyperthermia increases the

sensitivity of cancer cells towards radiation. It can also harm the cancer cells that are not

affected by radiation. When used in combination with radiation therapy, a gap of one

hour is maintained between the administrations of each treatment. The effects of certain

anti-cancer drugs are also increased through treatment by hyperthermia.

3.4 Types of Hyperthermia

There are 3 types of hyperthermia as described below.

Regional Hyperthermia In this type various approaches are used to heat large areas of

tissue, like cavity, organ or limb.

17



o Deep tissue in this one external applicators is positioned around the body cavity

or organ to be treated, and microwave or radiofrequency energy is focused on the

area to raise its temperature.

o Regional perfusion techniques are used for arms and legs, such as melanoma, or

cancer in some organs, In this one, patient’s blood is removed, heated, and then

refused back into organ. Usually anticancer drugs are given in this treatment.

o Continuous hyperthermic peritoneal perfusion (CHPP) is a technique used to treat

cancers within the peritoneal cavity (the space within the abdomen that contains

the intestines, stomach, and liver), including primary peritoneal mesothelioma and

stomach cancer. During surgery, heated anticancer drugs flow from a warming

device through the peritoneal cavity. The peritoneal cavity temperature reaches

106–108°F.

Local hyperthermia In this type, heat is applied to a small area, such as a tumor, using

various techniques that deliver energy to heat the tumor. Different types of energy may

be used to apply heat, including microwave, radiofrequency, and ultrasound. There are

several approaches to local hyperthermia, depending on the location of tumor. [5]

18



3.5 Types of Hyperthermia Treatment

o External techniques are for tumors which are just below the skin. In this one,

external applicators are positioned around or near the appropriate region, and

energy is focused on the tumor to raise its temperature.

o Intraluminal methods are used to treat tumors within or near body cavities, such

as the esophagus. Probes are placed inside the cavity and inserted into the tumor

to deliver energy and heat that area directly.

o Interstitial techniques are used to treat tumors deep within the body, such as brain

tumors. This technique allows the tumor to be heated to higher temperatures than

external techniques. Under anesthesia, probes or needles are inserted into the

tumor. Imaging techniques, such as ultrasound, may be used to make sure the

probe is properly positioned within the tumor. The heat source is then inserted

into the probe. Radiofrequency ablation is a type of interstitial hyperthermia that

uses radio waves to kill cancer cells.

Whole-body hyperthermia: In this type of hyperthermia cancer that has spread

throughout the body has been treated. This can be done with techniques that increase

the body temperature to 107–108°F, including the use of thermal chambers or hot

water blankets. [6]

19



3.6 Side effects of Hyperthermia

Most normal tissues are not damaged during hyperthermia if the temperature remains

under 111°F. However, due to regional differences in tissue characteristics, higher

temperatures may occur in various spots. This can result in burns, or pain. Perfusion

techniques can cause tissue swelling, blood clots, bleeding, and other damage to the

normal tissues in the perfuse area; however, most of these side effects are for short

period. Whole-body hyperthermia can cause more serious side effects.

3.7 Future scope for Hyperthermia

To be considered for standard treatment, Hyperthermia had few challenges to overcome.

Many clinical trials are being conducted to evaluate the effectiveness of hyperthermia.

Some trials continue to research hyperthermia in combination with other therapies for the

treatment of different cancers. Other studies focus on improving hyperthermia

techniques.

20



Chapter 4

DESIGN AND SETUP OF S-BAND RECTANGULAR HORN ARRAY

The photograph of the 3-element array is shown below in Figure 4.1. The array

consists of a central focusing horn antenna, which is the red antenna and has aperture

dimensions of 30 cm x 22 cm. The central focusing is flanked on either side by two

directing horn antennas, which are the yellow antennas and have the same aperture

dimensions of 21.9 cm x 15 cm. [9]

Figure 4.1 Photograph of 3-element horn array set up in Lab

In the earlier work [Give reference here to earlier project] the array shown in the photograph

above was studied extensively by performing many experiments on each of the elements and

also on the whole array. These earlier results are detailed briefly below for explanation.

21



4.1 Measurement of near-field of single horn Antenna along the axis of the antenna

The schematic diagram for the laboratory setup is shown in Figure 4.2 below for a single

horn antenna measurement. The probe, or receiving antenna, was a wideband spiral antenna,

which is applicable at the current S-band frequency range.

Figure 4.2 Experimental set up for single element antenna

In this measurement the x-y position of the receiving probe antenna is fixed along the

axis of the array (x = y = 0 cm), and the probe position is varied along the axial or z-

position at 5mm intervals for a 10 cm range. The measured results of B/A or –A/B (dB)

are detailed in Table 1 of Appendix A1, and a plot of the results is given below in figure

4.3

22



5 6 7 8 9 10 11 12 13 14 15-39

-38.5

-38

-37.5

-37

-36.5

-36

-35.5

-35

-34.5

Figure 4.3 Axial near-zone electric field of single horn antenna

4.2 Measurement of Z-Axis Near Field of 3 Element Horn Antenna Array

This section details the experimental studies carried out on three-element S-band antenna

array of rectangular horn antennas.

The schematic diagram for the laboratory setup is shown below in Figure 4.4. The

transmitting antennas were placed side by side horizontally with their outer edges

touching with each other. The receiving probe antenna was placed along the center of

horn antennas with x and y position of the receiving antenna fixed and varied along the z-

axis at intervals of 5mm for a 10cm range.

23

z, cm

Electric field,

dB



Figure 4.4 Experimental setup for 3-element horn array with 3 elements in line

Similarly z-axis measurements were carried out for two other positions of the central

focusing element of the array: first with the central array element 5.08 cm behind outer

directing elements, as shown in Figure 4.5 and secondly with the central array element

10.16 cm behind outer directing elements, as shown in Figure 4.6.

24



Figure 4.5 Experimental setup for 3-element horn array with central element 5.08

cm behind outer directing elements

In this set-up, port 1 of the network analyzer is connected to the feed network which

splits into three branches. The current splits in these branches and is fed to the horn

antennas. The receiving probe is connected to port 2 of the network analyzer. In the

above figure, the center antenna is 5.08 cm behind the other two elements.

25



Figure 4.6 Experimental setup for 3-element horn array with central element 10.16

cm behind outer directing elements

The set-up here is similar to that of Figure 4.5 with only a difference of the center

antenna being placed 10.16 cm behind the other two elements.

The consolidated measured results for all the three positions of the center antenna are

shown in Figure 4.7 on next page. It can be clearly noted that the position of the peak

electric field moves backward as the antenna is moved backward.

26



-42

-40

-38

-36

-34

-32

-30

0 . 0

1 . 0

2 . 0

3 . 0

4 . 0

5 . 0

6 . 0

7 . 0

8 . 0

9 . 0

1 0 . 0

z, cm

E l e c t r i c

f i e l d ,

d B

z = 0 cm

z = -5.08 cm

z = -10.16 cm

Figure 4.7 Consolidated beam focusing demonstration for 3-element horn array

4.3 Experimental Characterization of current distribution in the feed network

Each path or branch of the feed network was connected across the two terminals of the

network analyzer while matching the other ports with a 50 Ohm load. The following S matrix

was obtained in the network analyzer while measuring the current distribution in the feed

network.

[ -10.39∟52 -5.5∟96 -10.22∟25 -9.98∟-30

-6.5∟97 -10.6∟10 -10.51∟31 -13∟3

-10.68∟13 -11.06∟19 -14.95∟162 -4.8∟95

-10.6∟-41 -12.8∟15 -6.15∟96 -15.9∟42 ]

The above S matrix can be used to find the current flowing through each branch of the feed

network.

27



Chapter 5

SIMULATION RESULTS OF S-BAND RECTANGUALR HORN ARRAY

This chapter details the comparison between theoretical and earlier measurement

studies carried out on a three element S-band horn array [9]. All the simulation studies

were done using the Ansoft HFSS, and this was the first project completed in our

laboratory using the new software.

5.1 HFSS setup, simulation and array parameters

The simulation parameters are as follows:

Frequency of simulation: 2.4 GHz

Excitation method: current

Array current distribution: [0.7 1.0 0.7]

Horn antenna material: copper

Simulation environment: air

The schematic, the near field pattern and the electric field distribution as seen in the

HFSS environment is shown below in the following figures. There are three cases

obtained by varying the position of the center element. They were simulated and the

changes in the electric field peak positions were observable.

28

z, cm



Case 1: In the following three figures, the three array elements are in line

Figure 5.1a HFSS schematic when all elements are in line

The above figure also shows the electric field in V/m along a line of 30 cm centered

along the Z axis. The highest electric field point was noted in this figure and a plane

perpendicular to z axis was placed on that point. The next figure shows us the intensity of

the electric field in the XY plane. The peak was found to be at a distance of

approximately 1 cm from the open end of the horn antenna. So a plane was placed at this

point and the electric field intensity on this plane was generated using HFSS. The

maximum electric field intensity is 561 V/m and the minimum electric field intensity is

27.3 V/m in the plane shown on next page.

29



Figure 5.1b Electric field along a XY plane at the highest field point

Figure 5.1c Near field pattern (Actual distance=30 cm) all horn antennas are in line

30



Figure 5.1c is a rectangular plot of the near field measured along a line of 30 cm. The

maximum electric field is 53.8 dB at a distance of 13.2 cm from the origin.

Case 2: In the following three figures, the center array element is 5 cm behind the other two elements



along the Z axis. The maximum electric field intensity is 434 V/m and the minimum

electric field intensity is 21.4 V/m

31



Figure 5.2b Electric field along a XY plane at the highest field point

The highest electric field point was noted in the previous figure and a plane perpendicular

to z axis was placed on that point. This figure shows us the intensity of the electric field

in the XY plane. The peak was found to be at a distance of approximately 1 cm from the

open end of the horn antenna. So a plane was placed at this point and the electric field

intensity on this plane was generated using HFSS. The maximum field is 475 V/m and

the minimum field is 22.6 V/m.

32



Figure 5.2c Near field pattern (Actual distance=30 cm) center element is 5 cm behind the

other two elements

The above figure is a rectangular plot of the near field measured along a line of 30 cm.

The maximum electric field is 53.9 dB at a distance of 0.9 cm from the origin. It can be

noted that the peak has moved toward origin when compared with the Figure 5.1c. This

shows that the peak moves toward backward as the center horn antenna is moved

backward.

33



Case 3: In the following three figures, the center array element is 10m behind the other

two elements



along the Z axis. The maximum electric field intensity is 401 V/m and the minimum

electric field intensity is 45.6 V/m

34



Figure 5.3b: Electric field along a XY plane at the highest field point

The highest electric field point was noted in the previous figure and a plane perpendicular

to z axis was placed on that point. This figure shows us the intensity of the electric field

in the XY plane. The peak was found to be at a distance of approximately 19 cm from the

open end of the horn antenna. So a plane was placed at this point and the electric field

intensity on this plane was generated using HFSS. The maximum field is 419 V/m which

is at the center and the minimum field is 11.8 V/m at the edges.

35



Figure 5.3c Near field pattern (Actual distance=30 cm) center element is 10 cm behind the

other two elements.


The maximum electric field is 52.6 dB at a distance of 19.4 cm from the origin.

5.2 HFSS simulation with new parameter

Now a parameter in the simulation was changed. It is as follows

Array current distribution: [0.7 1 0.7] was changed to [0.85 1 0.85].

This change was made because practically this is the ratio in which the current is divided

in the feed network although theoretically it is the former ratio. The following near field

patterns for three cases were obtained on simulating with array currents [0.85 1 0.85].

36



Figure 5.4 a: Near field pattern (Actual distance = 30 cm) all elements are in line


The maximum electric field is 53.7 dB at a distance of 12.7 cm from the origin. This

pattern was obtained when the current distribution ratio was changed to 0.85:1:0.85.

37



Figure 5.4b: Near field pattern (Actual distance = 30 cm) center element is 5 cm behind the

other two elements



pattern was obtained when the current distribution ratio was changed to 0.85:1:0.85. The

center horn antenna was placed 5 cm behind the other 2 antennas.

38



Figure 5.4c: Near field pattern (Actual distance = 30 cm) center element is 10 cm behind the

other two elements



pattern was obtained when the current distribution ratio was changed to 0.85:1:0.85. The

center horn antenna was placed 10 cm behind the other 2 antennas.

It was noted that there was no significant difference in the position of the peak electric

field with the change in array current distribution from [0.7 1 0.7] to [0.85 1 0.85]

39



Comparison of measured and simulated array performance

Table 5.1 compares the HFSS simulation with the measured data obtained previously for

the earlier work [9]. The table compares the peak values of the beam obtained during

measurement and simulation for all three configurations of the array.

Array Configuration HFSS Simulation Peak

Value (cm)

Measured Peak value (cm)

All elements in line 13.3 5

Central element 5.08 cm

behind outer elements1 3

Central element 10.16 cm

behind outer elements

19.4 1.1

Table 5.1 Comparison of Measured and Simulated data

There is a significant difference between the simulated results and the measured data.

When the elements are in line, the difference between the measured and the simulated value

is 8.3 cm. When the center element is 5.08 cm behind, both the simulated and the measured

results show a reduction in the distance between the antenna and the peak field. But still there

is a difference of 2 cm in the positions of the peak field. When the center element is moved

10 cm behind the other two elements, in the measured result, the peak field moves closer to

the antenna whereas the peak field moves further away from the antenna in the simulated

40



result. It is also noted that there were two peaks; one at the line at which the outer elements

are placed (0 cm) and the other peak is at 19.4 cm.

One of the causes for these differences is due to presence of other lab equipments

while measuring data and due to human interference - the person’s proximity to the

transmitting and receiving antennas. Another cause for the difference would be due to the

fact that HFSS computes the results in a adaptive fashion - runs multiple times to find the

accurate solution and it is possible that the number of adaptive solutions chosen to compute

these results are not sufficient. Yet another cause would be loose connections between the

connectors of the network analyzer while measuring data.

41



Chapter 6

CONCLUSION AND SCOPE FOR FUTURE WORK

This project was aimed at the accurate simulation of the near-field effects of a 3-

element rectangular horn array antenna operating in the S-band frequency range of 2.45

GHz. This frequency has applications in medical field such as microwave hyperthermia,

where focused microwave radiation is used to treat tumors. In an earlier project, the array

was designed, assembled and its near-field performance was measured on the HP 8720C

Network Analyzer in the CSUS Microwave Laboratory. Currently, the simulation effort

is to model the array performance by using the HFSS software, and to match the earlier

measured results.

The simulation results differed slightly from the measured results but showed that

clear beam formation is obtained in the near-field of the array. Additionally, the results

also exhibited the beam control of the array, with the beam being capable of being

adjusted over a 5 cm axial range. Two-dimensional planar measurements and simulation

studies were also conducted to validate the volumetric focusing properties of the array.

The latter results also showed clear beam focusing in the planar x-y plane of the array.

Future work will focus on improving the efficiency of the array, with an aim to

increase the resolution of the beam so that much clearer focus can be obtained for

hyperthermia applications. This would involve trying out different current distributions

for the array elements, which can be achieved by the use of attenuators in the feed section

of the array.

42



REFERENCES

[1] E.L. Jones, J.R. Oleson, L.R. Prosnitz, T.V. Samulski, Z. Vujaskovic, D.Yu, L.L.Sanders, and M.W. Dewhirst, “Randomized trial of hyperthermia and radiation for superficial tumors”, J Clin. Oncol. 2005 May 1;23(13):3079-85.

[2] Manual of ANSOFT HFSS ver 11.0, ANSOFT, 2007

[3] “Hyperthermia and heat related illness: Question – Answers” retrieved fromhttp://www.medicinenet.com/hyperthermia/article.htm#1 on Nov 2 2009.

[4] “Valley Center Institute: Information” retrieved from: http://www.vci.org

on Oct.28 2009

[5] Maluta S, Dall'Oglio S, Romano M, Marciai N, Pioli F, Giri MG, Benecchi PL,

Comunale L, Porcaro AB., “Conformal radiotherapy plus local hyperthermia in patients affected by locally advanced high risk prostate cancer: preliminary results of

a prospective phase II study”, Int J Hyperthermia. 2007 Aug; 23(5):451-6.

[6] “Hyperthermia in Cancer Treatment: Questions and Answers” retrieved from:

http://www.cancer.gov/cancertopics/factsheet/Therapy/hyperthermia, on Nov. 3 2009

[7] “Hyperthermia centers: Information” retrieved from:

http://www.geocities.com/HotSprings/Villa/5443/alts/hytherm.html , on Nov 8 2009

[8] David M Pozar “Microwave Engineering” Third edition, Wiley Publication, Year

2003

[9] Sridhar Nayakwadi, Lakshmi B.T.V, “Near-Field Beam Forming for Medicalapplications using S-band rectangular horn antenna array”. Master of Science Project,

Department of Electrical and Electronics Engineering, August 2008.

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http://www.geocities.com/HotSprings/Villa/5443/alts/hytherm.html

http://www.geocities.com/HotSprings/Villa/5443/alts/hytherm.html

master's_project report_dhara and thomas

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