Simulation of Near-Field Generated by S-Band Rectangular Horn Antenna Array for Hyperthermia Therapy Applications Using 4Nec2 Software

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SIMULATION OF NEAR-FIELD GENERATED BY S-BAND RECTANGULAR HORN ANTENNA ARRAY FOR HYPERTHERMIA THERAPY APPLICATIONS USING 4NEC2 SOFTWARE

Dwija Reddy Aloori B.Tech, J N T University, India, 2008

Sandhya Ramagiri B.Tech, J N T University, India, 2008

PROJECT

Submitted in partial satisfaction of the requirements for the degrees of

MASTER OF SCIENCE

COMPUTER ENGINEERING

and

ELECTRICAL AND ELECTRONIC ENGINEERING

CALIFORNIA STATE UNIVERSITY, SACRAMENTO

FALL 2010 SIMULATION OF NEAR-FIELD GENERATED BY S-BAND RECTANGULAR HORN ANTENNA ARRAY FOR HYPERTHERMIA THERAPY APPLICATIONS USING 4NEC2 SOFTWARE

A Project

Dwija Reddy Aloori

Sandhya Ramagiri

Approved by:

______, Committee Chair Preetham B. Kumar, Ph.D.

______, Second Reader Russell Tatro, M.S.

______Date

Students: Dwija Reddy Aloori Sandhya Ramagiri

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.

______, Department Chair ______Suresh Vadhva, Ph.D. Date

Department of Computer Engineering

Department of Electrical and Electronic Engineering

iii

Abstract

SIMULATION OF NEAR-FIELD GENERATED BY S-BAND RECTANGULAR HORN ANTENNA ARRAY FOR HYPERTHERMIA THERAPY APPLICATIONS USING 4NEC2 SOFTWARE

Dwija Reddy Aloori

Sandhya Ramagiri

This project will focus on the application of advanced electromagnetic simulation

software 4nec2, for the near-field characterization of a 3-element S-band array of horn antennas, operating at the ISM frequency of 2.4 GHz. Previous modeling efforts have

shown a significant difference between simulated and measured data. The key effort in

this project will be to minimize the difference between simulated and measured data

using 4nec2 software. This study has useful application in the area of clinical

hyperthermia, which is defined as the therapeutic treatment of tumors in the body by

heating caused by focused RF or microwave radiation. The 3-element array 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.

, Committee Chair Preetham B. Kumar, Ph.D

______Date

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.

We are extremely thankful to Mr. Russell Tatro our second reader, for reviewing this work and for his valuable suggestions in improving the same. It is our duty to recognize the efforts of Computer Engineering and 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

Computer Engineering Department who have been encouraging us throughout our curriculum.

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 ...... viii

List of Figures ...... ix

Chapter 1. INTRODUCTION ...... 1

2. HYPERTHERMIA TREATMENT AND ITS APPLICATIONS ...... 3 2.1 Introduction to Hyperthermia ...... 3 2.2 Types of Hyperthermia ...... 4 2.3 Risks of Hyperthermia ...... 6 2.4 Effects of Hyperthermia ...... 7 2.5 Future Scope of Hyperthermia ...... 8

3. NUMERICAL ELECTRO MAGNETICS CODE(4NEC2) ...... 9 3.1 Introduction to 4NEC2 ...... 9 3.2 Additional Features of 4NEC2 ...... 10 3.3 4NEC2 Project Flow ...... 10 3.4 Configuration ...... 11 3.5 Steps for drawing a geometrical model ...... 11

4. DESIGN AND SETUP OF S-BAND RECTANGULAR HORN ARRAY ...... 17 4.1 Measurement of near field of single horn antenna along the axis of the antenna ....18 4.2 Measurement of Z-axis near field of three element horn antenna array ...... 19

5. SIMULATION RESULTS OF S-BAND RECTANGULAR HORN ARRAY ...... 24 5.1 4NEC2 Setup, simulation and array parameters ...... 24 5.1.1 All array elements in the same line ...... 25 5.1.2 Center array element is 5.08cm behind the other two elements ...... 30 5.1.3 Center array element is 10.16cm behind the other two elements ...... 35 5.2 Comparison of measured and simulated array performance ...... 40

6. CONCLUSION AND SCOPE FOR FUTURE WORK ...... 43

References ...... 45

vii

LIST OF TABLES Page

1. Table 5.1 Comparison of Measured and Simulated data……………………………41

viii

LIST OF FIGURES Page

1. Figure 3.1 Main window ...... 12

2. Figure 3.2 Geometry edit window ...... 13

3. Figure 3.3 Geometry edit window showing voltage source at a point ...... 13

4. Figure 3.4 Geometry edit window showing frequency/ground selection ...... 14

5. Figure 3.5 Geometry edit window showing conductivity and dielectric constant ...... 15

6. Figure 3.6 To calculate the NEC output data ...... 15

7. Figure 3.7 Window showing selection of pattern ...... 16

8. Figure 3.8 Window showing near field pattern and its equivalent values ...... 16

9. Figure 4.1 Photograph of 3-element horn array set up in Lab ...... 17

10. Figure 4.2 Experimental set up for single element antenna ...... 18

11. Figure 4.3 Axial near-zone electric field of single horn antenna ...... 19

12. Figure 4.4 Experimental setup for 3-element horn array with 3 elements in line ... 20

13. Figure 4.5 Experimental setup for 3-element horn array with central element 5.08 cm behind outer directing elements ...... 21

14. Figure 4.6 Experimental setup for 3-element horn array with central element 10.16 cm behind outer directing elements ...... 22

15. Figure 4.7 Consolidated beam focusing demonstration for 3-element horn array .... 23

16. Figure 5.1a 4NEC2 schematic when the center waveguide is in line with other two elements ...... 25

17. Figure 5.1b 4NEC2 input .nec file when all array elements are in the same line .... 26

18. Figure 5.1c Electric field intensity when all waveguide elements are in line ...... 27

19. Figure 5.1d Rectangular plot of near field pattern when all array elements are in line ...... 28

20. Figure 5.1e Electric field along a YZ plane at the highest field point ...... 29

21. Figure 5.1f 4NEC2 schematic when the center element is 5.08cm behind the other two elements ...... 30

22. Figure 5.1g 4NEC2 input .nec file when the center element is 5.08cm behind the other elements ...... 31

23. Figure 5.1h Electric field intensity when the center element is 5.08cm behind the other elements ...... 32

24. Figure 5.1i Rectangular plot of near field pattern when center element is 5.08cm behind the other elements...... 33

25. Figure 5.1j Electric field along a YZ plane at the highest field point ...... 34

26. Figure 5.1k 4NEC2 schematic when the center element is 10.16cm behind the other two elements ...... 35

27. Figure 5.1l 4NEC2 input .nec file when the center element is 10.16cm behind the other two elements ...... 36

28. Figure 5.1m Electric field intensity when the center element is 10.16cm behind the other two elements ...... 37

29. Figure 5.1n Rectangular plot of near field pattern when center element is 10.16cm behind the other two elements...... 38

30. Figure 5.1o Electric field along a YZ plane at the highest field point ...... 39

31. Figure 5.1p Rectangular plot of near field pattern comparing three cases ...... 40

Chapter 1

INTRODUCTION

Microwaves are short electromagnetic waves with smaller wavelength. This

definition comes from Pozar's text "Microwave Engineering" [1], 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)”. The boundaries between far infrared light,

microwaves and ultra-high-frequency radio waves are fairly arbitrary depending on the

type and field of study. Microwave components have a wide variety of applications

ranging from communications to imaging, remote sensing and heating methods due to their unique characteristics. Along with such widespread applications, microwaves are also used in certain niche applications such as medical diagnosis and treatment. This area of research has been gaining pace and moving towards solving the growing needs of medical science.

Two important components associated with the microwave electric field are far- field and near-field. The region far from the antenna is known as far-field, where the energy from the antenna is radiated only along the radial direction. This energy finds its applications mostly in communication systems. Secondly, the region close to antenna is known as reactive near-field, where the energy is stored in electrical and magnetic field but is not radiated from them. It has its applications in primarily targeting the medical imaging and therapy techniques.

Microwave Hyperthermia is an important near-field application of electromagnetic energy, using the S-band frequency range 2.45 GHz which is accurately

suitable for heat absorption [2, 4-7]. Hyperthermia is a treatment where 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 to avoid heat

radiation in surrounding areas of the tumor. This is the point where accurate antenna

setup and formation of conformal microwave antenna radiation is required. Hyperthermia

is generally used with other standard forms of cancer treatment, such as radiation and

chemotherapy

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 by adjusting

the position of the central focusing element of the array. The theoretical simulations are

done using the 4Nec2 software [2], developed by Arie Voors [3].

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

outlines the background on clinical hyperthermia therapy in cancer treatment. Chapter 3

describes the 4Nec2 software. Chapter 4 gives details of the three-element array simulation for different focusing points along the axis of the array. Chapter 5 gives

simulation results of the three-element waveguide and antenna array using 4NEC2 software. Chapter 6 gives conclusions from the results obtained and direction for future work, followed with the references.

Chapter 2

HYPERTHERMIA TREATMENT AND ITS APPLICATIONS

Hyperthermia is a method to treat cancer in tissues by raising the temperatures in tumors to the range of 42ºC - 45ºC. The word Hyperthermia, meaning overheating the body, is made up of "hyper" (high) and "thermia" from the Greek word "thermes" (heat). [9].

Earlier hyperthermia application in the eighties focused on hyperthermia as a standalone treatment, however, currently it is found to be more effective as an adjuvant to conventional cancer therapies such as radiation and chemotherapy [2].

2.1 Introduction to Hyperthermia

Depending on many factors, microwave frequencies are more dominant in therapeutic applications such as tissue heating. It is considered as the most promising method in hyperthermia treatment of cancer, with side effects and discomfort levels for the patient being very minimal. However, the major challenge in microwave hyperthermia is to generate a very narrow beam possible to heat only the affected body parts while protecting the surrounding healthy tissues.

In clinical hyperthermia, heat is applied locally to tumors, by raising tumor temperature to about 42.5ºC (108ºF) for about 45 to 60 minutes. This improves blood circulation, makes tumor cells more susceptible to radiation therapy and kills 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. [2, 7]

Different types of hyperthermia (local, regional, whole-body), discussed briefly

below, are based on the methodology for treatment and type of energy used to apply heat,

including microwave, radiofrequency and ultrasound. [6]

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] strongly suggest 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.

2.2 Types of Hyperthermia

There are different kinds of hyperthermia presently under study :

1. Local Hyperthermia

2. Regional Hyperthermia

3. Whole Body Hyperthermia

Local hyperthermia: Heat is applied to a small area, such as a tumor, using various techniques that deliver energy to heat the tumor. Different kinds of energy may be used to apply heat, including microwave, radiofrequency, and ultrasound. There are several approaches in local hyperthermia, depending on the location of tumor which are

discussed briefly below. [8]

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

external applicator is placed around or near the appropriate region and energy is

focused on the tumor to raise its temperature.

. 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.

. 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.

. Radiofrequency ablation (RFA) uses high-energy radio waves for treatment and

is most widely used in local hyperthermia. A needle probe is placed into the

tumor for few minutes 10 to 15 min which releases high temperatures (122º F and

212 ºF) and destroys the cancer cells.

Regional Hyperthermia: Various approaches are used to heat large areas of tissue, like cavity, organ or limb.

. Deep tissue approach uses external applicators that are positioned around the

body cavity or organ to be treated and microwave or radiofrequency energy is

focused on the area to raise its temperature.

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

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

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

. 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.

Whole-body hyperthermia: In this method, 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]

2.3 Risks of Hyperthermia [6]

Often, 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 also might harm 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 anticancer drugs are also increased through treatment by hyperthermia.

Several other risks associated with hyperthermia include pain, external burns,

minor discomfort to significant pain due to high temperature, blistering and actual

burning of the skin. Studies have also suggested that for pregnant women, hyperthermia involves high risks in the form of birth defects called neural tube defects in the babies.

Further hyperthermia can cause miscarriage, high fever and heart defects and abdominal wall defects for the new born infants. The risks involved with whole body hyperthermia are more which includes cardiac and vascular disorders, diarrhea, nausea and vomiting.

Extracorporeal systemic hyperthermia can cause frequent persistent neurophites, abnormal blood coagulation, damages to liver and kidneys, and brain hemorrhaging and seizures. [12]

All these risks and side effects involved with hyperthermia are very rare, negligible and further can be avoided with careful and precisely controlled clinical procedures.

2.4 Effects of Hyperthermia

Possible side effects of hyperthermia depend on the technique being used and the part of the body being treated. Many normal tissues are not damaged during hyperthermia if the temperature remains under 111°F. Hyperthermia carries approximately a 5-10% chance of developing a condition called "fat necrosis,"[8] which can leave a hardened area of tissue or lump(s) under the skin and is usually permanent. Areas of fat necrosis are typically tender at first; however, the tenderness almost always goes away. These areas are not cancerous and can be biopsied for reassurance. Most side effects are short-term, while few result in serious issues. Local or regional hyperthermia can cause pain at the site, infection, bleeding, blood clots, swelling, burns, blistering, and damage to the skin,

8 muscles, and nerves near the treated area. Whole-body hyperthermia can cause nausea, vomiting, and diarrhea. More serious, though rare, side effects can include problems with the heart, blood vessels, and other major organs. Other side effects less commonly include blood pressure fluctuations, blisters on the skin, superficial ulcers, bleeding or infection may develop after hyperthermia. Results show that experience, improved technology, and better skills in using hyperthermia treatment have led to fewer side effects, and in most cases the problems that people do have are not serious. [8]

2.5 Future Scope of Hyperthermia

The use of hyperthermia in the treatment of cancers is appealing because, as a physical therapy, hyperthermia would have far fewer restrictive side effects than chemotherapy and radiotherapy, and it could be used in combination with these therapies. However, the currently available modalities of hyperthermia are often limited by their inability to selectively target tumor tissue and, hence, they carry a high risk of collateral organ damage or they deposit heat in a much localized manner which can result in under- treatment of a tumor. Magnetically mediated hyperthermia (MMH) has the potential to address these shortcomings which can be improved along with other studies. Clinical trials are being conducted to evaluate the effectiveness of hyperthermia. Many milestones need to be crossed before hyperthermia can be considered a standard treatment for cancer.

Chapter 3

NUMERICAL ELECTRO MAGNETICS CODE (4NEC2)

3.1 Introduction to 4NEC2 simulation software

4NEC-2 designed by Arie Voors, is a windows based tool for creating, viewing,

optimizing and checking 2D and 3D style antenna geometry structures; generate, display

and compare near/far-field radiation patterns for both starting and experienced antenna

modeler [3]. In this project, 4NEC-2 ver. 5.8.1 was used, which has the following

features: [3]

. Graphical 2D and 3D visualization of Far- and Near-field data and Geometry

structures.

. Drag and drop style Geometry Editor to assist the starting antenna modeler.

. Capable of running up to 11000 wires and/or segments (limited by the max of 2Gb of

windows on-board memory)

. Sophisticated real-time 3D geometry and pattern viewer showing real wire-radius.

. Interactive Smith chart visualization for freq-sweeps.

. Geometry builder to create cylinder, patch, plane, box, helix and parabola shaped

structures using auto-segmentation and/or equal-area rules.

The user is 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. 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.

3.2 Additional Features of 4NEC2:[3]

• Software based on the mininec code

• Calculating near and far fields

• 3D patterns for both geometry and fields

• Extensive library of antennas

• Built in optimizer

• Compare patterns

As mentioned above, 4NEC2 software has extensive features related to antenna

modeling. Many predefined functions from the 4NEC2 library are also available to use in

the project. The built in optimizer in 4NEC2 helps in getting a better design by

comparing different patterns obtained in the result and choosing the most suitable among

them.

3.3 4NEC2 Project Flow

Every 4NEC2 project follows these steps

• Configuration

• Drawing

• Source/Load

• Frequency

• Environment

• Solution

• Plot

3.4 Configuration:

To configure 4NEC2 5.8.1 following steps should be followed.

Click 4NEC2 5.8.1 to start the design

Click: File Open 4nec2 in/output file  filename (Takes you to a folder where there are many built in designs. Open any one of them)

Click: Settingsselect NEC editor (new).

Click: A new window will open showing all the coordinates of the geometrical structure

which can be edited. If we want to model a new structure from here following steps

should be followed:

Click: File New  Save asfilename

Now, a new design interface has 3 sub-windows: Main window, geometry window and

geometry edit window.

3.5 Steps for drawing geometric model: [5]

On windows machine, on opening 4NEC2 5.8.1, the main window appears as the one

below:

Figure 3.1 Main window

The next step would be to draw the geometrical structure. Click Edit  Input (.nec) file. The following window called geometry edit window will open:

Figure 3.2 Geometry edit window

The next step is to specify the type of source/load whether it is voltage or current and also specify the coordinates of the point where exactly we want to insert the source/load. For example if your source is voltage then following window shows the selection of voltage source:

Figure 3.3 Geometry edit window showing voltage source at a point

The next step in the design is to specify the frequency/ground. The following figure shows the selection of the frequency/ground:

Figure 3.4 Geometry edit window showing frequency/ground selection

If you choose real ground then you need to specify the ground type, conductivity and dielectric constant. The following figure shows that:

Figure 3.5 Geometry edit window showing conductivity and dielectric constant

The next step in the design is to calculate the radiation pattern and other patterns. The following procedure is to be followed:

Figure 3.6 To calculate the NEC output data

Now if we want to get far field pattern select the far field pattern and click generate as follows:

Figure 3.7 Window showing selection of pattern

Following results show up:

Figure 3.8 Window showing near field pattern and its equivalent values

Chapter 4

DESIGN AND SETUP OF S-BAND RECTANGULAR HORN ARRAY

The arrangement of the 3-element array setup is shown in Figure 4.1 below. 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. [11]

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

In the previous student project [8], the array setup shown above was studied extensively by performing many experiments on each of the elements and also on the whole array, to

18 measure the near-field patterns along the axis, and in the plane of maximum electric field.

These earlier results are detailed briefly below for explanation.

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) plotted below in Figure 4.3

-34.5

-35

-35.5

-36 Electric -36.5field, dB

-37

-37.5

-38

-38.5

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

z, cm

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

4.2 Measurement of Z-Axis near-field of three 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 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.

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.

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.

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 below. It can be clearly noted that the position of the peak electric field moves backward as the central focusing antenna is moved backward.

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 -30

-32

-34

z = 0 cm -36 z = -5.08 cm

Electric field, dB field, Electric z = -10.16 cm

-38

-40

-42 z, cm

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

Chapter 5

SIMULATION RESULTS OF S-BAND RECTANGULAR HORN ARRAY

This chapter details the simulations study performed on the S-band array, and also provides comparison between the measured and simulation results of the array. The simulation studies were done using the 4NEC2 3-dimensional electromagnetic simulation software.

5.1 4NEC2 setup, simulation and array parameters

The simulation parameters of the array are as follows:

Frequency of simulation: 2.4 GHz

Excitation method: Current

Source/Load: voltage source (1+j0) V

Simulation environment: Free space

The schematic of the array and, the near field patterns of the array that are generated using 4NEC2 software are discussed here with relevant figures for the same. As mentioned earlier we consider three cases of the waveguide array, firstly with all elements in line and the other two are obtained by changing the position of the center element.

5.1.1 Case 1: All the array elements are in the same line

In this section the center element of the array is placed in line with the other directing elements. This implies that the radiating apertures of the three horn antennas are in the same y-z plane and the following figure 5.1a indicates the geometrical structure of the above discussed configuration.

Figure 5.1a 4NEC2 schematic when the center waveguide is in line with other two elements

The Input .nec file showing the dimensions of the geometrical structure is shown below in Figure 5.1b. The geometry file contains the data on how the horn array elements are created, and excited by the required current distribution. Each horn antenna is constructed

by using the P-rectan element for the flat waveguide section, and the P-quadri element for the flared horn section.

Figure 5.1b 4NEC2 input .nec file when all array elements are in the same line

The simulated results of the above geometrical structure using 4NEC2 are shown below

in Figure 5.1c to 5.1e. The simulation results include the resultant electric field of the

array along the axis of the array, and also in the perpendicular sectional plane corresponding to the position of peak electric field along the axis.

Figure 5.1c below shows the electric field distribution along the x-axis of the coordinated system. The color bar gives the range of values of the electric field.

Figure 5.1c Electric field intensity when all waveguide elements are in line

Figure 5.1d shows the same axial electric field distribution in a graphical fashion, which clearly shows the peaks in the electric field distribution.

Figure 5.1d Rectangular plot of near field pattern when all array elements are in line

From the figure 5.1d above, it can be observed that the highest electric field is

670.9459V/m obtained at a point 0.442 m from the origin. The following figure 5.1e shows the 2-dimensional y-z plot of the electric field distribution at the plane corresponding to the peak electric field position along the axis i.e. x = 0.442 m

Figure 5.1e Electric field along a YZ plane at the highest field point

From the above figure, we can see that the minimum electric field intensity is 132 V/m and the maximum is 295 V/m.

5.1.2 Case 2: Center array element is 5.08 cm behind the other two elements

In this section the center element of the array is moved backward by 5.08cm to the other directing elements. This implies that the radiating apertures of the three horn antennas are in the same y-z plane and the following figure 5.1f indicates the geometrical structure of the above discussed configuration.

Figure 5.1f 4NEC2 schematic when the center element is 5.08cm behind the other two elements

The Input .nec file showing the dimensions of the geometrical structure is shown below in Figure 5.1g. The geometry file contains the data on how the horn array elements are

created, and excited by the required current distribution. Each horn antenna is constructed

by using the P-rectan element for the flat waveguide section, and the P-quadri element for the flared horn section.

Figure 5.1g 4NEC2 input .nec file when the center element is 5.08cm behind the other elements

The simulated results of the above geometrical structure using 4NEC2 are shown below

in Figure 5.1h to 5.1j. The simulation results include the resultant electric field of the

array along the axis of the array, and also in the perpendicular sectional plane

corresponding to the position of peak electric field along the axis.

Figure 5.1h below shows the electric field distribution along the x-axis of the coordinated system. The color bar gives the range of values of the electric field.

Figure 5.1h Electric field intensity when the center element is 5.08cm behind the other

elements

Figure 5.1i shows the same axial electric field distribution in a graphical fashion, which clearly shows the peaks in the electric field distribution.

Figure 5.1i Rectangular plot of near field pattern when center element is 5.08cm behind other elements

From the figure 5.1d above, it can be observed that the highest electric field is 177.0207

V/m obtained at a point 0.616 m from the origin. The following figure 5.1j shows the 2- dimensional y-z plot of the electric field distribution at the plane corresponding to the peak electric field position along the axis i.e. x = 0.616 m

Figure 5.1j Electric field along a YZ plane at the highest field point

From the above figure it can be observed that the minimum electric field intensity is 76.2

V/m at and maximum electric field intensity is 180 V/m.

5.1.3 Case 3: Center array element is 10.16 cm behind the other two elements

In this section the center element of the array is moved backward by 10.16cm to the other directing elements. This implies that the radiating apertures of the three horn antennas are in the same y-z plane and the following figure 5.1k indicates the geometrical structure of the above discussed configuration.

Figure 5.1k 4NEC2 schematic when the center element is 10.16cm behind the other two elements

by using the P-rectan element for the flat waveguide section, and the P-quadri element for the flared horn section.

Figure 5.1l 4NEC2 input .nec file when the center element is 10.16cm behind the other elements

The simulated results of the above geometrical structure using 4NEC2 are shown below

in Figure 5.1m to 5.1o. The simulation results include the resultant electric field of the array along the axis of the array, and also in the perpendicular sectional plane corresponding to the position of peak electric field along the axis.

Figure 5.1m below shows the electric field distribution along the x-axis of the

coordinated system. The color bar gives the range of values of the electric field.

Figure 5.1m Electric field intensity when the center element is 10.16cm behind the other elements

Figure 5.1n shows the same axial electric field distribution in a graphical fashion, which clearly shows the peaks in the electric field distribution.

Figure 5.1n Rectangular plot of near field pattern when center element is 10.16cm behind other elements

From the figure 5.1m above, it can be observed that the highest electric field is

93.62569V/m obtained at a point 0.715 m from the origin. The following figure 5.1o shows the 2-dimensional y-z plot of the electric field distribution at the plane corresponding to the peak electric field position along the axis i.e. x = 0.715 m

Figure 5.1o Electric field along a YZ plane at the highest field point

From the above figure it can be observed that the minimum electric field intensity is 34.5

V/m and maximum electric field intensity is 142 V/m.

5.2 Comparison of measured and simulated array performance

The consolidated axial electric field distribution patterns for all three array configurations are shown below in Figure 5.1p.

Figure 5.1p Rectangular plot of near field pattern comparing three cases

Table 5.1 below compares the 4nec2 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.

4nec2 Simulation Peak Measured Peak value Array Configuration Value (m) (m)

All elements in line 0.834-0.448=0.386 0.05

Central element 5.08 cm behind outer

elements 0.616-0.448=0.168 0.03

Central element 10.16 cm behind outer

elements 0.715-0.448=0.267 0.011

Table 5.1 Comparison of Measured and Simulated data

NOTE: The values of the horn for practical measurements are taken at the end of the antenna, while the values of the horn for simulated measurements are taken from the start of the antenna. Hence, the difference measurement (0.448m) is subtracted for accurate comparison between the simulated and measured values.

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 0.259m. When the center element is 5.08cm 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 0.3m in the positions of the peak field. When the center element is moved

10.16cm behind the other two elements, in the measured result, the peak field moves closer to the antenna whereas the peak moves further away from the antenna in the simulated result.

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 the 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 4NEC2 software, 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 showed 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.

There is scope for significant future work on the project especially 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. This is essential in hyperthermia systems

44 where power should be predominantly focused on the tumor area with minimum power to the neighboring healthy tissue.

REFERENCES

[1] David M Pozar “Microwave Engineering” Third edition, Wiley Publication, Year 2003

[2] 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.

[3] 4NEC2 Tutorial by Arie Voors for ver 5.8.1. http://home.ict.nl/~arivoors/Home.htm on July 8 2010.

[4] “Hyperthermia in Cancer Treatment: Questions and Answers” retrieved from: http://www.cancer.gov/cancertopics/factsheet/Therapy/hyperthermia , on Nov. 3 2009

[5] “Valley Center Institute: Information” retrieved from: http://www.vci.org on Oct.28 2009

[6] 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.

[7] “Hyperthermia and heat related illness: Question – Answers” retrieved from http://iv.iiarjournals.org/content/23/1/143.full www.medicinet.com/hyperthermia/article.html on July 11, 2010. http://www.pamf.org/radonc/tech/hyperthermia.html

[8] Sridhar Nayakwadi, Lakshmi B.T.V, “Near-Field Beam Forming for Medical applications using S-band rectangular horn antenna array”. Master of Science Project, Department of Electrical and Electronics Engineering, August 2008.

[9] Wust P et al., ‘Hyperthermia in combined treatment of cancer’, The Lancet Oncology, 2002; 3: 487–497