MICROWAVE ENGINEERING

Transcription

1 MICROWAVE ENGINEERING (Including Measurement Techniques and Lab. Mannual) PROF. P.K. CHATURVEDI M.Tech., Ph.D; M.B.A.(U.K.) Dean Skyline Institute of Engg. & Tech. Greater Noida (U.P.) Formerly Director in GOI, GITM, Ggn. & Amity University An ISO 9001:2008 Certified Company 2/25, Ansari Road, Darya Ganj

2 MICROWAVE ENGINEERING Copyright VAYU EDUCATION OF INDIA ISBN: First Edition: 2014 Price: ` 260/- All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the Publishers. Published by: VAYU EDUCATION OF INDIA 2/25, Ansari Road, Darya Ganj, New Delhi Ph.: , Fax: vayueducation@rediffmail.com, vayueducation1@gmail.com Web:

3 PREFACE Unprecedented growth in the application of microwave has taken place during the last two-three decades, especially in mobile communication, TV transmission, Industrial/domestic applications, satellite communication, telemetry, Radars and other navigational aids etc. This rapid development of microwave along with digital technologies have synergized and further accelerated the growth rate. This has created an increased demand for trained engineers in civilian as well as in defence organizations. This book will meet the needs of the students of engineering courses i.e. BE, B.Tech, MSc (Tech), MTech (Microwaves), MSc (Electronics), etc. However the students need to have prior knowledge of electromagnetics. This book contains (a) fundamental concepts and principles behind microwave engineering in a simple and student friendly lucid language, keeping a balance between physical and analytical approach (b) Contains a large number of solved/unsolved problems, for developing practical knowledge after every chapter. (c) Over 300 diagrams with a special effort put in, for giving numerical values in the graphs and dimensions of components/devices, in order to get a real feel/visualization of that microwave device, as this has been found to be missing in most of the books. The figures have full explanations for making it complete in itself. (d) Additional feature of laboratory manual of 14 Simple experiments, giving full theory, procedures, precautions and sample of readings expected with each experiment, followed by quiz/viva question for the benefit of the students as well as the faculty. The book consists of 8-Chapters along with an annexure giving related constants and the index. The Chapter-1 introduces the subject along with the concepts of CW/ Pulsed signals, decibel, anechoic chamber, EMI/EMC etc. Chapter-2 summarizes the basics of wave propagation in the transmission lines and waveguides. Chapter-3 covers cavity resonators while Chapter-4 describes over 16 varieties of components used in microwaves. Chapters 5 and 6 cover various type of microwave signal generators and amplifiers. Chapter-5 firstly covers limitations of conventional tubes and then the microwave tubes, e.g. klystron tubes, magnetron, TWT etc. Chapter-6 extensively covers 4-types of transistors, 8-types

4 (vi) of diodes, with applications. Chapter-7 covers measurements techniques of important parameters and related instruments. Chapter-8 gives 14-most-important experiments of microwave engineering. I am very much thankful to my life partner and children, who have been source of inspiration and provided me congenial atmosphere even in odd hours, with useful suggestions, while writing the manuscript and proof reading of the book. I am thankful to Dr. Raj Kumar, my PhD Student (who is now Director of a prestigious Engineering College, Rewari), for his valuable assistance in the initial phase of the book. I thank Mrs. Sapna Sharma, Faculty of SIET, Gr. Noida, for giving the initial prompting-material of this book. I am thankful to Mr. Chandeep Singh of m/s NVIS Technologies Pvt. Ltd, for providing soft copies of the figures of microwave products. I am also thankful to the authors of various books (as per list of references), which I have referred during the long period I have been teaching this subject in various institutions. Finally, I convey my sincere thanks to M/s Vayu Education of India, the Publisher of this book, for their painstaking and sincere efforts for bringing the book in a standard and excellent form. However, if you notice any mistake, error or discrepancy, it would be appreciated, if the same is brought to our notice. You may please send your valuable suggestions, feedback for improvement of the book. Prof. P K Chaturvedi New Delhi pkchat.book2@gmail.com

5 TABLE OF CONTENTS Preface (v) CHAPTER 1: INTRODUCTION TO MICROWAVES Introduction History of Microwaves Characteristic Features and Advantages of Microwaves CW and pulsed microwave power Decibel A unit to measure relative power, voltage level etc Anechoic Chamber: The e.m. radiation free area Electromagnetic interference (EMI) and Electro-magnetic compatibility (EMC) Radiation Radiation hazards for human body/birds etc Application areas of microwaves Summary 13 Review Questions CHAPTER 2: WAVE GUIDES AND STRIP LINES Introduction Propagation of waves in the transmission line Wave guides circular and rectangular Propagation of waves in rectangular wave guide TE Waves in Rectangular Waves Guides, Electrical Field and Magnetic Field Equations Non Existence of TEM Mode in Waveguide TM Waves in Rectangular Wave Guide : Electric and Magnetic Field Equation Cut off Frequencies of Dominont Modes and Degenerate Modes in TE/TM Wave Mode-Excitation in Rectangular Wave Guides Wave Impedance in TM and TE Waves Power Transmision and Losses in Wave Guide 38

6 (viii) Breakdown Power and Power Handling Capacity in rectangular Wave Guide Guide Wave length, Group Velocity and Phase Velocity Propagation In Circular Waveguides TE Waves in Circular Waveguide E and H Field Equations TM Modes in Circular Waveguide: E and H Field Equations Cut-Off Wavelength in Circular Waveguide, Dominant and Degenerate Modes Phase Velocity, Group Velocity, Guide Wavelength and Wave Impedance in Circular Waveguides Power Transmission and Attenuation Loss in Circular Waveguide Power Handing Capacity and Break Down Power Limits in Circular Waveguides TEM Wave in Circular Waveguide do not exist Excitation of Modes Advantages, Disadvantages and Applications of Circular Waveguides Strip Lines and Micro Strip Lines Microwave Component using Strip Lines 60 Solved Problems Review Questions CHAPTER 3: MICROWAVES CAVITY RESONATORS Introduction Rectangular Waveguide Resonators Circular wave guide Resonators Coaxial LIne Resonators Re-Entrant Cavity Resonator Cylinderical hole-and-slot cavity resonator Microstrip line Resonators Coupling of Cavities with the line: Reflection and transmission types Coupling Factor Frequency Tuning of Cavity The Q factor of a cavity resonator 88 Solved Problems Review Questions CHAPTER 4: MICROWAVES COMPONENTS AND THEIR SCATTERING MATRICES Introduction Coaxial Cables and Connectors Microwave waveguide junctions: Types 104

7 (ix) 4.4 H-Plane Tee junction (Current junction) E-Plane Tee junction (Voltage junction) E-H Plane Tee (Hybrid junction/magic Tee) Applications and limitations of magic T Hybrid Ring (rat-race junction) Directional Couplers For power Sampling/Testing Various types of directional couplers Bends, Twists and Transitions Attenuators and terminators Iris and Screw Posts for Impedance Matching/Introducing L or C Signal Tapping/Feeding and Detecting Probes and loops (for tapping/exciting/feeding μw power into a wave guide or for taking out microwave power from the wave guide) Diode Detectors Wave meters/frequency Meter Faraday rotation and Ferrite Devices-Isolators, Gyrators and circulators Isolator Gyrator Circulators Phase shifters 147 Solved Problems Review Questions CHAPTER 5: MICROWAVE TUBES AS MICROWAVE SOURCE (OSCILLATORS) AND AMPLIFIERS Introduction The conventional tubes High frequency limitations of conventional tubes Inter electrode capacitance-shoriting the signal Lead Inductance impeding the Signal Transit Time Effect Much Larger than μw time period Gain band width product limitations RF losses (I 2 R losses) in wire & skin effect Dielectric Loss Radiation Loss Microwave tubes Oscillators and Amplifiers Thier Classfication Klystrons Two Cavity Klystron Amplifier Two Cavity Klystron Oscillator Reflex Klystron Oscillator Travelling wave tubes (TWT) amplifier Backward Wave oscillator (BWO) Magnetron oscillator 196 Solved Problems Review Questions

8 (x) CHAPTER 6: MICROWAVE SEMI-CONDUCTORS DEVICES- OSCILLATORS, AMPLIFIERS AND CIRCUIT DEVICES Introduction Classification of microwave semiconductor devices Microwave Transistors-BJT and FET Microwave Bipolar junction transistor (BJT) Junction Field effect transistors (Jn-FET) Metal-semiconductor field effect transistor (MESFET) Metal oxide field effect transistor (MOSFET) Tunnel diode characteristic, And working oscillators & amplifiers Tunnel Diode Amplifier and Oscillators Transfered Electron Devices (TED)-Gunn Diodes Introduction-bulk Device With No Junctions Gunn Effect: Two valley theory (Ridley Watkins Hilson theory for ve resistance) Moving High Field Dipole Domain in the Device and the phase difference in I and V Four Modes of Gunn Device Operation as oscillator Diode Structure and packaged Diode The Gunn Oscillator and Amplifier Circuits Application of Gunn Diode Oscillators and Amplifiers Typical Characteristics Avalanche Transit time Devices IMPATT and TRAPATT IMPATT Diode, Read Diode Oscillator and Amplifier TRAPATT Diode Oscillators BARITT Diodes oscillator Schottky Barrier diodes (SBD)-As Detector & Mixer PIN diode for switching/controling microwave power, Phase shifting, modulating etc PIN diode application in circuits (as switch, attenuator, phase shifter, limiter and AM unit) Varactor diode as a variable capacitor Varactor as Harmonic Generator/Frequency Multiplier Parametric Amplifier-An amplifier with up/down convertion of frequency Manley Rowe-Relation and types of Paramps Advantages, Limitations and Application of Paramps in General 288 Solved Problems Review Questions

9 (xi) CHAPTER 7: MICROWAVE MEASUREMENTS INSTRUMENTS AND TECHNIQUES Introduction Basic Microwave Bench Measurement Devices and Instruments Microwave Sources and their Power Supplies Isolator Frequency Meter or Wave Meter Variable Attennator Slotted Line and Tunable Detector and Probe System VSWR Meter Power Meter Spectrum Analyser Network Analyser Measurement Techniques in Microwaves Measurement of Frequency and Wave Length Measurement of Power (V. Low, Low, Medium and High) Measurement of VSWR (Low, Medium and High) Measurement of Impedance (Pure Resistive and Complex) Insertion loss, attenuation loss and return loss Q-of a cavity: reflection and transmission types Measurement of Phase Shift by Comparision with precision Shifter Measurement of Dielecric Constant (ε r )-Minima shift due to dielectric Measurement of Noise figure and Noise factor by standard noise source and noise meter 326 Solved Problems Review Questions CHAPTER 8: SIMPLE LAB-EXPERIMENTS AND LAB MANUAL Experiment. No. 1 : Study of reflex klystron characterstic modes of power and frequency with repeller Voltage-electronic tuning. 333 Experiment No. 2 : Calibration of mechanical tuning screw of reflex klystron. 341 Experiment No. 3 : Study of power mode characterstic of reflex klystron on CRO. 344 Experiment No. 4 : To determine frequency, wavelength and VSWR using slotted line.346 Experiment No. 5 : To determine high VSWR by double minima method. 350 Experiment No. 6 : To measure an unknown impedance using slotted line method. 353 Experiment No.7 : To study Gunn Diode characteristics and modulation depth using PINdiode Modulator. 357

10 (xii) Experiment No. 8: To Study E-plane Tee and H-plane Tee characteristics-isolation and coupling coefficients. 364 Experiment No.9: To Study Magic-Tee characteristics-isolation and coupling coef. 368 Experiment No. 10: To Study the characteristics of directional coupler-isolation and coupling coef. 372 Experiment No.11: To calibrate a variable attenuator using VSWR meter. 377 Experiment No. 12: Measurement of dielectric constant and phase shift by it. 380 Experiment No. 13: To study the ferrite devices isolator and circulator. 384 Experiment No. 14: To measure the Q-factor of resonant cavities-reflection type and transmission type. 388 References 393 Appendix Index

11 Chapter 1 INTRODUCTION TO MICROWAVES 1.1 Introduction 1.2 History of Microwaves 1.3 Characteristic features and advantages of microwaves 1.4 CW and pulsed microwave power 1.5 Decibel-A unit to measure relative power, voltage level etc. 1.6 Anechoic Chamber the em-radiation free area 1.7 Electro-magnetic interference (EMI) and Electro-magnetic Compatibility (EMC) 1.8 Radiation hazards for human body/bird etc. 1.9 Application areas of microwaves 1.10 Summary Review questions 1.1 INTRODUCTION Microwave is a descriptive term used to identify electromagnetic waves in the frequency spectrum ranging approximately from 1 GHz (wavelength λ = 30 cm) to 300 GHz (λ = 1 mm). For wavelength from 1.00 mm to 0.3 mm i.e., for frequencies 300 GHz to 1000GHz the em waves are called mili-meter waves (Fig 1.1) and submili-meter waves. Microwaves are so called as they are normally defined in terms of their wavelength. In fact beyond audio waves, all are electromagnetic waves having E-vector and H-vector which are perpendicular to each other. These waves have several interesting and unusual features, not found in other portions of the electromagnetic frequency spectrum. These features make microwaves uniquely suitable for several useful applications. Since the wavelengths are small, the phase varies rapidly with distance in the guided media; therefore the techniques of circuit analysis and design, measurements of power generation and amplification at these frequencies are different from those at lower frequencies.

12 2 Microwave Engineering Analysis based on Kirchhoff s laws and Ohms law (voltage-current) concepts are not easily possible for describing the circuit s behavior at microwave frequencies. It is necessary to analyze the circuit or the component in terms of electric and magnetic fields associated with it. For this reason microwave engineering is also known as electromagnetic engineering or applied electromagnetic. A background of electromagnetic theory is a pre-requisite for understanding microwaves. The complete spectrum of electromagnetic waves is given in fig 1.1 and 1.2 giving frequency and corresponding wavelength. It also gives names of different frequency bands (e.g. IEEE band, millimeter band, sub-millimeter of UHF & VHF etc.), different applications, guided media of application etc. The IEEE defined band is also given separately in Table 1.1. Audio Wave (type) Radio Microwave Infrafred Visible Ultraviolet X-Ray Gamma- Ray Cosmic rays Longer Wave-length (metres) Shorter Approximate Equivalent size (Comparison with wave length) A town Football field Humans Butterfly Pin Head Bacteria Virus Molecules Atoms Atomic Nuclei Electron Audio waves Infrared Lower Frequency-Hz(Waves per second) Shorter Visible Light ultra violet 1-micro meter (micron) = 10 6 meter,1mm = 10 9 meter, 1 Angstron = m (AºU) Fig. 1.1: Comparative visualisation of the complete spectrum of em-wavelengths and its frequencies Table 1.1: Microwave frequency band-ieee names Frequency Band designation 3-30 MHz HF MHz VHF GHz UHF 1-2 GHz L 2-4 GHz S 4-8 GHz C 8-12 GHz X GHz Ku GHz K GHz Ka GHz millimeter > GHz sub-millimeter

13 Introduction to Microwaves 3 Guided media (In addition to space) Frequency Spectrum, Bands Guided media & Application Optical fibre Waveguides 7.5 mm Satellite Comunication RADAR etc. TV, Police aviation Ultransonic Water media (submarine) Vel. of e.m. wave in free space = c = f = 3 10 met/sec. λ c/s submarine Fig. 1.2: Frequency Spectrum: Audio and em waves: guided media and applications

14 4 Microwave Engineering 1.2 HISTORY OF MICROWAVES Michael Faraday JC Maxwell J.C. Bose One of the first attempts to deduce the fundamental law of electromagnetic action in terms of an electric field, propagating at finite velocity was done by Karl Friedrick Gauss ( ), a German mathematician. However the genesis of microwave & electro-magnetic waves in general, can be taken from the Michael Faraday s (1848) experiments on propagation of magnetic disturbance (em-waves), which latter got theoretical formulation by James Clerk Maxwell(1865), popularly known as Maxwell s Field Equations. There after Marconi and Hertz in their experiments (1888), proved the Maxwell s theory of rf-signal being an em-wave and travel with the velocity of light (c = λ. f = metre/sec). In 1885, J.C. Bose developed a circuit for generating microwave power and in 1898 developed horn antenna, polariser and detector of r.f.-signal, which is used even today. The slow but steady development in the area of transmission line, transmitters etc. continued till 1930, but thereafter it got accelerated. The genesis of microwave propagation through waveguides was from the success of Dr. Southworth (1933) of AT & T labs of USA, when he was

15 Introduction to Microwaves 5 able to transmit signal through metal pipe of 4 diameter. Thereafter the requirements of World War I & II further boosted through the development of microwave tubes - Klystron by Varian brothers (1936) of Stanford University, Magnetron by Randel & Boots of UK(1939), Radar by Henry Tizard (UK) during 1940 etc. Thereafter also the development continued and ferrite devices, TWT etc came in 1950s. In 1960s, Solid-State-Microwave sources e.g Gunn diodes, avalanche-diodes, microwave transistors etc came in full swing, which takes very small space and has very law D.C. power requirements for generating microwave power. Now application of microwaves has entered all the segments of Communication & Telemetry control (audio, video, text & data), whether it is for use in civilian systems or in defense systems or for space applications. It has other applications also e.g. heating (in Industrial processes or domestic appliances or cancer treatment), microwavespectroscopy, radio astronomy, satellite communication etc. Today for microwave power requirements below 5W, we can use sources of semiconductor devices like IMPATT diode etc., while for higher power requirements we use microwave tubes like Klystron, Magnetron, Travelling Wave Tube (TWT) etc. 1.3 CHARACTERISTIC FEATURES AND ADVANTAGES OF MICROWAVES Unique features and hence advantages of microwave over low frequency signal are as 1. Increased bandwidth availability: It has large bandwidth because of high frequency. Normally the maximum bandwidth can be 10% of the base signal. A 10% bandwidth at 3 GHz implies availability of 300MHz bandwidth and hence much more information can be transmitted. 2. Lower Fading and reliability: Fading effect is high at low frequency, while in microwave due to line of sight propagation and high frequency, there is less fading effect and hence microwave communication is more reliable. 3. Transparency property: It has transparency property i.e. it can easily propagate through air, space even through an ionized layer surrounding the earth and atmosphere, leading to important applications like Astronomical research of space. Duplex communication between ground station and speed vehicles. The only GHz frequency band which is less used due to molecules resonance (H 2 O and O 2 ) absorption. Above 400 GHz, some frequencies are blocked by ozone in the atmosphere. 4. Low Power requirements: The power required by the transmitter and receiver at microwave frequency is quite low as compared to low frequency operations

16 Microwave Engineering By P.K. Chaturvedi Publisher : Vayu Education ISBN : Author : P.K. Chaturvedi Type the URL : Get this ebook