i

Dissertation Title

DESIGN AND ANALYSIS OF HIGH-POWER ELECTROMAGNETIC

IMPULSE RADIATOR

Submitted

In partial fulfillment of the requirements of the degree of

Doctor of Philosophy (Electrical Engineering)

by

SACHIN BHAGWAT UMBARKAR

(Reg. No.119030002)

Programme: Ph.D. Electrical Engineering (Technical)

Admitted in: 2011

Guide/Supervisor

DR. H. A. MANGALVEDEKAR

February 2015

Department of Electrical Engineering

VEERMATA JIJABAI TECHNOLOGICAL INSTITUTE

(Autonomous Institute Affiliated to University of Mumbai)

Mumbai-400019

ii

DECLARATION

We declare that this written submission represents my ideas in my own words and where others‟

ideas or words have been included, I have adequately cited and referenced the original sources.

We also declare that I have adhered to all principles of academic honesty and integrity and have not

misrepresented or fabricated or falsified any idea / data / fact / source in my submission.

We understand that any violation of the above will be cause for disciplinary action by the Institute

and can also evoke penal action from the sources which have thus not been properly cited or from

whom proper permission has not been taken when needed.

Signature of the student

Sachin Bhagwat Umbarkar Dr. H. A Mangalvedekar

(Roll.No-119030002) (Supervisor)

Date:

iii

CERTIFICATE

This is to certify that Sachin Bhagwat Umbarkar, a student of Doctor of Philosophy

(Electrical Engineering), has completed the thesis entitled, “Design and Analysis of

High-Power Electromagnetic Impulse Radiator” to our satisfaction.

Dr. H. A. Mangalvedekar

Guide

Dr. R. N. Awale

Head, Electrical Department

Prof. O. G. Kakde

Director, VJTI

Seal and Signature

Date:

Place: VJTI, Mumbai

Seal:

iv

Approval Sheet

This thesis, “Design and Analysis of High-Power Electromagnetics Impulse Radiator”

submitted by Sachin Bhagwat Umbarkar (Roll no.119030002), is found to be satisfactory and is

approved for the Degree of Doctor of Philosophy in Electrical Engineering.

Dr. H. A. Mangalvedekar

Supervisor / Guide

Examiner Chairman

Date:

Place: VJTI, Mumbai

Seal:

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ACKNOWLEDGEMENT

With immense gratitude and respect, I would like to express genuine regards to my guide

Prof. H. A. Mangalvedekar and his wife Smt. Arundhati to bring this thesis to a successful

completion. I wish to articulate my heartfelt appreciation to Prof. O. G. Kakde (Director, VJTI),

Prof. N. M. Singh, Prof. R. N. Awale (Head, Electrical Engg. Dept.), Prof. R. D. Daruwala, (Dean,

Academics), Dr. Meena Panse, Dr. Sushama Wagh, Prof. F. S. Kazi, Mr. H. B. Chaudhari, Mr.

Krishna Kanakgiri, Mrs. Pragati Gupta, Mr. S. Sawant of VJTI for their valuable guidance and

constant support to nurture the best in me.

I would like to particularly give special thanks to the project sponsors from DAE-BRNS

(Department of Atomic Energy, Board of Research in Nuclear Science) for funding this project. I

am highly obliged to the entire team including Dr. L. M. Gantayet, Dr. A. K. Ray, Dr. Archana

Sharma, Mr. R. K. Rajawat, Mr. D. P. Chakravarthy, Dr. K. C. Mittal, Mr. P. C. Saroj, Ms. Ritu

Agrawal, Mr. Sandip Singh, Mr. S. Mitra, and the entire organization of Accelerator & Pulse Power

Division, Bhabha Atomic Research Centre and Electrons Beam Centre, Kharghar, for their

constructive guidance and experimental support. It gives me immense pleasure to thank the

international advisors Dr. D. V. Giri, Dr. William D. Prather, Dr. Everett G. Farr, Dr. Edl

Schamiloglu, Dr. Roger, Dr. Nicolas Mora for their informative discussion and motivation during

the international conference meetings. Thanks to the national advisors Dr. D. C. Pandey, Dr. Dhiraj

Singh, and Mr. Vijay Bhosale for their technical inputs.

The software support for this project was offered by various EM tools developers viz. CST

studio, SPICE, MATLAB and PIC-MAGIC-3D.

Prof. Bindu S., Dr. Amol and Mr. Mrunal have always extended their constant support,

technical knowledge, co-operation and encouragement.

I also want to take this opportunity to thank Shri. Radhakrishna Vikhe Patil (Minister,

Maharashtra state and Founder of Pravara Education Society) for providing the funding for my

work. My colleagues of Pravara Engineering College, Loni constantly extended their co-operation

during this work.

Earnest thanks to my friends; Ms. Winney Thomas, Ms. Sindhuja, Mr. Rizwan, Mr.

Abhishek, Mr. P. Soman, Mr. Anand, Mr. Aniket, Mr. Amol, Ms. Renu, Mr. Anupam, Mr. Paresh,

Mr. Mayur, Mr. Rachit, Mr. Ayush, Mr. Rahul, Mr. Vikram of VJTI for their encouragement.

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With an overwhelming warmth and deep respect I offer „Pranams’ to my dearest family

members, for always showing faith in me and my dreams. I feel blessed to have such parents who

have persistently supported and always encouraged and motivated me which helped me excel in my

work. Their serene patience was very much inspiring for the successful completion of this

dissertation.

Mr. Sachin Bhagwat Umbarkar

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ABSTRACT

Pulses with sub-nanoseconds / nanoseconds rise time are used in high power radar,

sterilization, testing the effect on electronic systems, food irradiation, electromagnetic welding,

waste water processing, defence, medical electronics etc. There are various methods for obtaining

the mentioned low rise time pulses. In this dissertation, a Marx generator, peaking capacitor and

peaking switch are used to obtain high amplitude low rise time pulse. A radiating antenna is then

connected to the output of peaking stage. Such a system is known as the high-power

electromagnetic (EM) impulse radiator. Two such EM radiators were mathematically analysed,

simulated, designed, fabricated and the experiments have been conducted in this dissertation.

In experiment -1 the system is made compact by mounting the peaking stage above Marx in

the same tank and pressurised with N2 gas up to 2 kg/cm2. The output of this stage is 6 ns rise-time

and 150 ns Full Width at Half Maxima (FWHM). This pulse is then fed to Half Transverse

Electromagnetic (HTEM) horn antenna. The radiated output of the antenna has 5.02 kV/m radiation

intensity at 15 m distance in the bore-sight with a 32 MHz frequency. The experiment was

simulated using Computer Simulation Technology (CST) Microwave studio software and it

matched with experimental results. The existing mathematical model of the literature has been

enhanced to include the effect of feeding height of the antenna. The experimental results has been

compared with the simulation results and are found to match precisely. It was further observed from

simulations that the HTEM antenna had significant back and side radiations which causes reduction

in the bore-sight radiation, gain and directivity of the antenna.

The experiment-2 was conducted to increase the radiation output. In this set up, the peaking

switch electrode mounting arrangement was modified, the pressure arrangement for Marx generator

and peaking stage were separated, the antenna was re-designed with reflector at the back and its

feed arms were reshaped to reduce the radiation loss. This antenna is called Folded-Feed Half

Impulse Radiating Antenna (FF-HIRA). The various configurations for this antenna feeding

arrangement are simulated in CST-MS software. The experimental output gave 1 ns rise time / 150

ns FWHM, voltage 240 kV peak amplitude. The peaking switch was pressured to 2 kg/cm2 and the

Marx tank was pressured to 0.5 kg/cm2. This experiment gave radiated E far field output of 14.4

kV/m at 15 m distance at 180 MHz frequency. These experimental results were found to be in good

agreement with the simulation results. The variation of E far field intensity for various distances is

viii

measured. The new peaking switch can be pressured to 8 kg/cm2 and the feeding arm has been

modified to increase the area of illumination. Comparisons of HTEM and FF-HIRA antenna are

presented and concluded with salient advantages of FF-HIRA over HTEM antenna.

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Table of Contents

Declaration of the Student……………………………………………………………………... ii

Certificate……………………………………………………………………………………... iii

Approval Sheet ...………………………………………………………………….................. iv

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

Abstract…………………………………………………………………………….................. vi

List of Figures………………………………………………………………………………… xii

List of Tables………………………………………………………………………………….. xvii

List of Abbreviations…………………………………………………………………………. xviii

Chapter 1 Introduction

1.1 Background ................................................................................................................... 1

1.2 Hyper-band definition (Full Bandwidth Classification) .................................................. 2

1.3 Hyper-band Generator ................................................................................................... 3

1.4 Motivation ..................................................................................................................... 5

1.5 Scope ............................................................................................................................. 6

1.6 Salient Contribution ....................................................................................................... 7

1.6.1 Contribution in HTEM horn type Antenna design ............................................... 7

1.6.2 Contribution in FF-HIRA design ......................................................................... 7

1.7 The organization of thesis .............................................................................................. 8

Chapter 2 Literature Survey

2.1 Introduction ................................................................................................................. 10

2.2 Marx generators and peaking stage .............................................................................. 11

2.3 TEM Horn antenna (including HTEM & Lens IRA) .................................................... 13

2.4 Reflector Type Impulse Radiating Antennas (IRAs) .................................................... 16

2.5 Antenna Definitions ..................................................................................................... 19

2.6 Role of Computation .................................................................................................... 23

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Chapter 3 Development of Compact Marx Hyper-Band System

3.1 Introduction ................................................................................................................. 25

3.2 Design of PFN based Marx generator........................................................................... 26

3.3 Marx Generator Design Steps ...................................................................................... 28

3.4 Calculation of capacitance ........................................................................................... 29

3.5 Calculation of inductance............................................................................................. 29

3.6 Output energy of the Marx generator ........................................................................... 30

3.7 Design of Peaking Capacitor ........................................................................................ 31

3.8 Testing and simulation of Marx Generator ................................................................... 32

3.9 Conclusions ................................................................................................................. 34

Chapter 4 Half Transverse Electromagnetic (HTEM) Antenna

4.1 Introduction ................................................................................................................. 35

4.2 HTEM Antenna Parameter Calculations ...................................................................... 36

4.3 Experiment .................................................................................................................. 40

4.4 Comparison of Experimental Results with CST Simulation ......................................... 45

4.5 Investigation of HTEM Antenna using CST-MS .......................................................... 47

4.6 Conclusion................................................................................................................... 50

Chapter 5 Development of New Compact Marx Hyper-Band System

5.1 Introduction........................................................................................................ .............51

5.2 Constructional Details of New Peaking Switch..............................................................52

5.3 Experiments.....................................................................................................................55

5.4 Conclusions.....................................................................................................................58

Chapter 6 Folded-Feed Half Impulse Radiating Antenna (FF-HIRA)

6.1 Introduction ................................................................................................................. 59

6.2 Experimental Setup of HIRA and TEM sensor ............................................................. 61

6.3 Terminating Resistor.................................................................................................... 62

6.4 Bore-sight Radiations .................................................................................................. 63

6.5 CST Modeling of HIRA ............................................................................................... 67

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6.6 Mathematical, Simulation and Experimental Results .................................................... 71

6.7 Performance Comparison of HTEM and HIRA ............................................................ 75

6.8 Fabrication details of half IRA ..................................................................................... 76

6.9 Conclusion................................................................................................................... 76

Chapter 7 Conclusions and Future Scope .........................................77

Publications ............................................................................................80

References ............................................................................................82

Appendix-1................................................................................... ............... 94

Appendix-2.................................................................................................103

Appendix-3.................................................................................................110

xii

List of Figures

Fig. No. Name of the figure Page No.

1.1. Block diagram of hyper-band generator 4

1.2(a)

3D Model of HTEM horn antenna 5

1.2(b) 3D Model of FF-HIRA 5

2.1 Extended Plate TEM horn 14

2.2(a) Tapered periodic wire 14

2.2(b) Tapered Periodic Slot 14

2.3 Lens IRA 15

2.4 Termination behind the horn antenna 16

3.1 300 kV compact Marx generator based on PFN 27

3.2(a) Marx generator with a peaking gap 27

3.2(b) Peaking capacitor enclosing the peaking gap mounted on Marx

generator

27

3.3 Marx generator and peaking capacitor enclosed with an SS chamber

with load, voltage divider and current shunt (50mΩ)

27

3.4 Schematic of Marx generator 28

3.5 PFN based Marx Capacitor 29

3.6 Equivalent circuit of the PFN based Marx generator after its erection 30

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3.7 Inductance measurement waveform (Time-200ns/div) 30

3.8 Peaking capacitor and Peaking gap arrangement 31

3.9 Output of 20 stages of the Marx generator in air (Pulse width-150 ns,

Rise time -25 ns, charging voltage -11.5 kV, and time/div-100 ns)

32

3.10 Output voltage and current pulse 32

3.11(a) Block diagram of the Marx generator with peaking capacitor 33

3.11(b) Simulated output voltage and current 33

3.11(c) Experimental results 33

4.1 Schematic of near field and far field region 36

4.2 Side view and Top view of antenna 37

4.3(a) The Characteristics impedance (Zc), of the HTEM horn antenna as a

function of the angles α and θa for (w/a<1) and without feeding height

38

4.3(b) The Characteristics impedance (Zc), of the HTEM horn antenna as a

function of the angles α and θa for (w/a<1) and with feeding height

38

4.4(a) The Characteristics impedance (Zc), of the HTEM horn antenna as a

function of the angles α and θa for (w/a>1) and without feeding height

(Hf)

39

4.4(b) The Characteristics impedance (Zc), of the HTEM horn antenna as a

function of the angles α and θa for (w/a>1) and with feeding height

39

4.5 Experimental setup of HTEM antenna 41

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4.6 Output of 20 stages of the Marx generator with peaking stage

(FWHM: 150ns, Vch: 24kV, RL: 160Ω, Time/div. 100ns, rise time:

3ns)

41

4.7 Magnetic Field Measurement Setup 42

4.8 Prodyne B-dot sensor model 42

4.9 H-far field using B-dot probe signal (20 mV/div) at 15 meter distance 43

4.10 E-far field using TEM sensor (2 V/div) at 15 meter distance 44

4.11 Marx Generator output pulse with peaking capacitor (rise time:

6.0122 ns)

45

4.12 Radiated E-field (far field) at 15 m distance for HTEM antenna 45

4.13 Scaled up version of the fig. 4.12 46

4.14 FFT of Radiated E-far field shown in fig. 4.12 46

4.15 Electric field variation in azimuthal direction 46

4.16 Electric field variation with respect to distance 47

4.17 Electric field variation with height from ground floor 47

4.18 Gaussian pulse with 1.44 ns rise time 48

4.19 [r.Efar/V]peak verses Antenna length (L) 48

4.20 [r.Efar/V]peak verses Antenna tapering angle (θa) L= 4.5 m, α=310 49

4.21 [r.Efar/V]peak verses Antenna flair angle (α) for L= 4.5 m, θa=250 49

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4.22 [r.Efar/V]peak verses Rise time for L=4.5 m, θa=230, α=250 49

5.1 Separate pressure arrangement for Marx tank and peaking switch 52

5.2 Auto CAD details of peaking switch 53

5.3 New Peaking Switch 54

5.4(a) Placement view 1: The Peaking Switch is place inside the Perspex Chamber

54

5.4(b) Placement view 2: The voltage divider of (1000:1) and Copper-

Sulphate (CuSO4) load.

54

5.5 Experimental output pulse from Marx (0.5 kg/cm2) + new peaking

stage (2 kg/cm2) (20 MHz Bandwidth), Voltage waveform (Green),

current waveform (red)

56

5.6(a) Experimental output pulse from Marx (0.5 kg/cm2) + new peaking

stage (2 kg/cm2) (250 MHz Bandwidth), Voltage waveform (green),

current waveform (red)

56

5.6(b) Scaled up of fig 5.6(a) (tr-1 ns) 57

5.7(a) Experimental output pulse from Marx (0.5 kg/cm2) + new peaking

stage (2 kg/cm2) (Full Bandwidth), Voltage waveform (Green),

current waveform (red)

57

5.7(b) Scaled up of fig 5.7(a) (tr-1 ns) 58

6.1(a) Experimental model of FF-HIRA measurements 61

6.1 (b-i) HIRA with spherical launching waveform 63

6.1 (b-ii) Half impulse radiating antenna with feeder arm inclination 66

6.2(a) 3D CST model of HIRA-1 67

6.2(b) 3 D CST Model of HIRA-2 67

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6.2(c) 3D CST model of HIRA-3 68

6.3 Gaussian feeding pulse of 500 ps rise time 68

6.4 Radiated field at 10 m distance has 26.92 kV/m field intensity for

500 ps Gaussian input feeding pulse by HIRA-2.

69

6.5 Variation of E far field intensity versus rise time of feeding pulse 69

6.6 Input feeding pulse generated by Marx generator + inbuilt peaking switch (tr: 6.0122ns)

70

6.7(a) Radiated far field intensity of 5 kV/m at 15 m distance. 70

6.7 (b) FFT of radiated far field intensity of HIRA-2 which has 90 MHz

dominant frequency.

70

6.8 Radiated E far field intensity indicating the pre-pulse and main-pulse 72

6.9 Experimental Setup along with HTEM setup. 73

6.10 Radiated field measured using TEM sensors at 15 m distance 73

6.11 Variation of E far field intensity versus bore-sight distance 74

xvii

List of Tables

Tab. No. Name of the table Page No.

1.1 Categories of HPEM signal based on percentage bandwidth 02

1.2 Categories of HPEM signals based on band ratio 03

2.1 Marx generators around the world 11

2.2 The year-wise development of Marx systems 12

2.3 Year wise figure of merit, source, switch type & antenna type. 20

3.1 Output Characteristics of Marx Generator 28

4.1 Specifications of the Prodyne B-24R probes 42

5.1 Table 5.2: Marx + New Peaking Switch performance for 3 mm inter

electrode gap (Appendix -1)

55

5.2 Table 5.2: Marx + New Peaking Switch performance for 0.5 mm inter

electrode gap (Appendix -2)

55

6.1 Three configuration of HIRA for CST-MS Modeling 67

6.2 Rise time versus E-far field at 10 m distance with Gaussian feeding

pulse of 300 kV peak amplitude.

69

6.3 Mathematical and Experimental values for E far field intensity 72

6.4 Achievable peak values of FoM (r.Efar) field and Gain-factor by experimentation

74

6.5 Comparison of HTEM and FF-HIRA 75

xviii

List of Abbreviations

Abbreviation Full-Form

br Band Ratio

CST-MS Computer Simulation Technology-Microwave Studio

FCC Federal Communication Commission

FIT Finite Integration Techniques

FWHM Full Width at Half Maxima

FF-HIRA Folded Feed – Half Impulse Radiating Antenna

FoM Figure of Merits

HPEM High-Power Electromagnetic

HTEM Half Transverse Electromagnetic

HV High-Voltage

kV kilo-Volts

m Meter

MV Mega-Volts

NEMP Nuclear Electromagnetic Pulse

ns Nanosecond

pbw Percentage Bandwidth

PFN Pulse Forming Network

PIC Particle In Cell

SSN Sensor and Simulation Notes

UV Ultraviolet

UWB Ultra-wideband

a Aperature height of HTEM antenna

A Magnetic vector potential

c Speed of light

CMarx Erected Marx capacitance

Ceq Equivalent capacitance

D Diameter of parabolic reflector

xix

Efar Electrical far field intensity

radE Radiated field

incE Incident field

E Marx total energy

F Focal length of reflector antenna

fH Higher Frequency

fL Lower Frequency

fg Normalised feed impedance

G Gain

Hfar Magnetic far field intensity

Io Marx output current

L Lenght of antenna

LMarx Erected Marx inductance

Leq Equivalent inductance

n Number of stages in Marx generator

N Number of elements per stage

R1 Outer radius of the inner cylinder

R2 Inner radius of the outer cylinder

Rf Distance from focal point to point of observation

Rload Load resistance

r Boresight distance

tr Rise time

To Marx output pulse duration

Vo Marx output voltage

Vc Marx charging voltage

( )incV t Antenna driving voltage

( )recV t Antenna received voltage

w Width of HTEM antenna

Zc Characteristic impedance

Zfeed Feed impedance

xx

Zo Intrinsic impedance

1z Unit vector along the z-direction

Ω Ohms

ε Permitivity

εr Relative Permitivity

μ Mobility

α Flair angle of HTEM antenna

θa Tapering angle of HTEM antenna