EC04 - 702: MICROWAVE DEVICES AND COMMUNICATION

By AJAL.AJ

Faculty , Dept of ECEMETS SCHOOL OF ENGINEERING,MALA

1. With this paper, student should be able to understand the working principle and use of various microwave components and semiconductor devices.

This paper also provides the basic aspects of terrestrial and satellite microwave communication

links

Objectives:

2.

Module I (13 hours) Basics of microwave Engineering

• Theory of waveguide transmission - rectangular waveguides - TE modes - TM modes - waveguide components - rectangular cavity resonator - circular cavity resonator (only basic ideas) - E-plane tee - magic tee - isolator - circulator -directional coupler - S matrix

Module II (13 hours)

Microwave tubes

• Microwave linear beam tubes - klystron (bunching, output power and loading) -reflex klystron - traveling wave tube (amplification process, convection current, axial electric field, gain) –

• Microwave crossed field tubes - magnetron (operation, characteristics and applications)

Module III (13 hours) Microwaves devices

• Semiconductor microwaves devices - microwave transistors - tunnel diodes and FETs - transferred electron devices - Gunn effect diodes - (Gunn effect, operation, modes of operation, microwave generation and amplification) - LSA diodes - InP diodes - Cd Te diodes - avalanche transit time devices - read diodes - impatt diodes - trapatt diodes - baritt diodes

Module IV (13 hours) Microwave communication

• Terrestrial microwave communication - basic principles of microwave links -link analysis - microwave relay systems - choice of frequency - line of sight and over the horizon systems - modulation methods - block schematic of terminal transmitters and receivers - effect of polarization - diversity receivers - digital microwave links - digital modulation schemes - fading - digital link design -satellite communication - orbit of communication satellites - angle of elevation - propagation delay - orbital spacing - satellite construction - transponders -antennas - multiple spot beams - earth station - link analysis - multiple accessschemes - digital satellite links

MODULE 1

Basics of microwave Engineering

Why Going For New Wave Why Going For New Wave guiding Structures guiding Structures

instead of transmission instead of transmission lineslines

??????

TE & TM ModesTE & TM Modes

Rectangular Waveguides Rectangular Waveguides (Derivation of fields EX ,Ey ,Hx & (Derivation of fields EX ,Ey ,Hx &

Hy)Hy)

Waveguide components

Rectangular waveguide

Waveguide to coax adapter

E-teeWaveguide bends

COORDINATES OF CIRCULAR CAVITY RESONATOR

METHODS OF EXCITATION

WHY GOING FOR SCATTERING PARAMETERS IN CASE OF

MICROWAVE NETWORKS ???

Waveguide Tees :

a.E Plane Teeb.H Plane Teec.Magic Tee

MICROWAVE HYBRID CIRCUITS

• MICROWAVE JUNCTION:

Interconnection of two or more devices

1.WAVE GUIDE TEES

2.DIRECTIONAL COUPLER

3.CIRCULATOR

MICROWAVE ISOLATOR

CIRCULATOR

Directional Coupler

Contrast the ideal & Contrast the ideal & practical directional practical directional coupler!!!coupler!!!

ideal ideal - infinite directivity - infinite directivity

practical practical directional coupler directional coupler

30 to 35 dB30 to 35 dB

TWO HOLETWO HOLE FOUR FOUR HOLEHOLE

SCHWINGERSCHWINGER BETHE HOLEBETHE HOLE

TYPES OF DIRECTIONAL COUPLERTYPES OF DIRECTIONAL COUPLER

Typical Directional Coupler Typical Directional Coupler constructed Using Micro strip constructed Using Micro strip LineLine

Typical Directional Coupler Typical Directional Coupler constructed Using RECT constructed Using RECT WAVEGUIDESWAVEGUIDES

MODULE 2

Microwave tubes

Microwave Tubes

• Used for high power/high frequency combination

• Tubes generate and amplify high levels of microwave power more cheaply than solid state devices

• Conventional tubes can be modified for low capacitance but specialized microwave tubes are also used

Evolution of microwave tubes

• 1935 – Heil oscillator• 1939 – klystron amplifier• 1944 – Helix type TWT• In the early 1950s – low power output of linear

beam tubes to high power levels• Finally invention of Magnetrons• Several devices were developed – two

significant devices among them are

1) extended interaction klystron2) Twystron hybrid amplifier

SIGNAL SOURCES THAT GENERATE POWER

Microwave tubes

@Frequency > 1GHz

E.g.: klystron, Traveling WaveTube, magnetron

conventional vacuum

tubes @

frequency < 1GHz

E.g. : triodes, tetrodes,

pentodes

What are all the constraints of ordinary vacuum tubes at

frequencies beyond 1 GHz????

The limitations of conventional vacuum tubes at frequencies

beyond 1 GHz :

• Lead inductance and inter electrode capacitance effects

• Transit Angle Effects

• Gain-Bandwidth product limitations

Types of Microwave Tubes

Linear beam tubes (O – Type)

Crossed Field Tubes (M – Type)

Eg: Klystron Reflex klystron TWT

Eg: Magnetron

Linear beam devices Crossed field devices

(I) Straight path taken by the electron beam

A principle feature of such tubes is that electrons travel in a curved path

(i) DC magnetic field is in parallel with DC electric field to focus the electron beam

DC magnetic field is perpendicular to DC electric field

Types of Linear Beam Tubes

TWYSTRON

MULTICAVITY KLYST

TWOCAVITY KLYST

LINEAR BEAM TUBES

KLYSTRON TUBES

HYBRID TUBES

TRAVELING WAVE TUBES

REFLEX KLYST

LADDE-RTRON

HELIX RING- BAR TWT

COUPLED CAVITY

TWT

HELIX BWO

TWYSTRON

• KLYSTRON + TWT = TWYSTRON

• It is hybrid amplifier that uses the combinations of klystron and TWT components

Velocity Modulation

PRINCIPLE

• Electric field from microwaves at buncher alternately speeds and slows electron beam .

• This causes electrons to bunch up Electron bunches at catcher induce microwaves with more energy.

• The cavities form a slow-wave structure

Magnetron Oscillator

TYPES OF TRAVELING WAVE MAGNETRON

• CYLINDRICAL

• LINEAR

• COAXIAL

• VOLTAGE-TUNABLE

• INVERTED COAXIAL

• FREQUENCY-AGILE COAXIAL

33

Narrow Pulse Magnetron SystemNarrow Pulse Magnetron SystemAt H6 Systems Before ShippingAt H6 Systems Before Shipping

2121

Narrow Pulse Magnetron SystemNarrow Pulse Magnetron SystemNaval Electromagnetic Radiation FacilityNaval Electromagnetic Radiation Facility

CHARECTRISTICS OF MAGNETRON ````

1. EFFICIENCY η = 40 to 70%

2. POWER OUTPUT ( 800KW )3. OPERATING FREQUENCY

( UPTO 10GHZ )

MODULE 3

Microwave Devices

Microwave Devices

• A semiconductor device for the generation or amplification of electromagnetic energy at microwave frequencies.

DEFINITION…

Leo EsakiThe Nobel

Prize in Physics 1973

A NEGATIVE RESISTANCE DEVICE

APPLICATIONS

• Because of negative resistance in the forward characteristics, the device can be used actively as an oscillator

• Tunnel diode symbol

- Ve Resistance Region

VfVp

Ip

Vv

Forward Voltage

Reverse voltage

Iv

Rev

erse

C

urr

ent

Fo

rwar

d C

urr

ent

Ip:- Peak Current; Iv :- Valley Current; Vp:- Peak Voltage

Vv:- Valley Voltage; Vf:- Peak Forward Voltage

I V - CHARACTERISTIC OF TUNNEL DIODE

p

V

GUNN DIODE

• Ridley and Watkins proposed in 1961• Hilsum calculated the transferred electron effect in III-V in 1962; experiment fails.• J.B. Gunn of IBM discovered the so-called Gunn effect in 1963 and rejected the above theory.• Kroemer explained the origin of the negative differential mobility is

Ridley-Watkins-Hilsum’s mechanism

Avalanche Transit-time DevicesATD ’s

• IMPATT Diode (IMPact IonizationAvalanche Transit Time Diode)

• TRAPATT diode (Trapped plasma avalanche triggered transit-time )

• BARRITT diode (Barrier injection transit-time diode )

READ DIODE

READ DIODE

• The basic operating principle of IMPATT diode can be understood by studying the structure proposed by READ in 1959 known as READ diode

• A read diode structure , doping profile and DC electric field distribution is shown in fig

READ DIODE

MICROWAVE CAVITY FREQUENCY TUNING

IMPATT DIODE

TRAPATT DIODES

Voltage & current

waveforms of trapatt

diode

BARRIER-INJECTION TRANSIT-TIME DIODE

BARITT

History

transit-time delay 에 의한 negative differential resistance 를 얻는 idea (Schockely ,1954)

additional phase delay 를 소개하기 위한 avalanche current 사용 (Read ,1958)

실험적으로 밝힘 (Johnston et al ,1965)

BARITT mode operation (Ruegg, Wright, 1968)

BARITT diode 를 처음으로 만듦 (coleman, Sze, 1971)

Structure

P-n junction, Schottky barrier, or 이 둘의 조합으로

Doping level : 0.5~10um

Substrate 는 low series resistance 때문에 변질됨

Series resistance 로부터 power dissipation 을 줄이기 위해서 가끔 substrate 는 10um 보다 두꺼워 짐

FGV

Characteristic

전압이 depletion edge meet 까지 가면 ,

punch-through 가 일어남

Junction 이 asymmetrical 하면 , Vpt≠V‘pt

이러한 characteristic 은 negative differential resistance or negative dV/dI 에서는 일어나지 않음

Characteristic Punch-through 에서 전압

Flat-band condition 에서 전압

V1= injecting junction 을 지나는 공급된 전압의 일부

Injection current

s

biD

s

Dpt

qNL

LqNV

2

2

2

s

DFB

LqNV

2

2

FB

FBIbi V

VVV

4

2

4

)(expexp*

1exp)(

exp*

22

2

FB

FBbpp

Ibibppp

kTV

VVq

kT

qTA

kT

qV

kT

qTAJ

Characteristic

Charge Q 가 주어진 후에 , saturation velocity 로 substrate 를 돌아다님

Terminal current

Frequency

L

QvI sat

L

vf sat

4

3

satv

Characteristic

Application Microwave generator

- tank circuit 에 connected, oscillator 는 dc source 로부터 microwave ac signal 로 바꿔줌

- microwave power source = burglar, proximity system

장점 – low noise level. Low voltage operation

단점 - reduced efficiency, lower output power

Voltage limiter

Related Device1) Double-Velocity Transit-Time diode (DOVETT)

• 유일한 특징은 saturation velocity가 두 가지 값을 가진다는 것

• Heterojunction

• Injection current - thermionic emission, tunneling

Related Device

2) Tunnel-Injection Transit-Time Diode ( TUNNETT )

• Injection current – tunneling (high field : 1MV/cm)

• structure – one junction

• Vicinity of injecting junction – higher doping level

• n+-layer – doping : 1019cm-3 , thickness : 10nm

• 장점 – high frequency capability (1000GHz), low voltage (2V)

Related Device3) Quantum-Well-Injection Transit-Time Diode

(QWITT)

• Injection current – tunneling

• Higher frequency (TUNNETT)

• negative differential resistance

Resonant tunneling mechanism

MODULE 4

Microwave communication

MODULE 4

• IT’S ALL ABOUT TWO COMMUNICATION SYSTEMS:

1. TERRESTRIAL MICROWAVE

COMMUNICATION SYSTEM

2. SATELLITE MICROWAVE

COMMUNICATION SYSTEM

140

History of Communication Satelite

• In 1964,the Intelsat Consortium was formed to operate and maintain the International Telecommunication Satellite System.

• In 1965,the first commercial satellite Intelsat I (Early Bird) was launched.

• In 1967-1968, it was followed by Intelsat II and Intelsat III respectively.

• In 1971, it was followed by Intelsat IV.• As of 1982, there were some 400 earth stations with over 55,000

channels using the Intelsat System.

19861980 1989 1992

Some of the everyday Technologies that depend on radio waves:

• AM and FM radio broadcasts • Cordless phones • Garage door openers • Wireless networks • Radio-controlled toys • Television broadcasts • Cell phones • GPS receivers • Ham radios • Satellite communications • Police radios • Wireless clocks

STRUCTURE OF ATMOSPHERE

Ion.. layers

IN IONOSPHERIC PROPAGATION

• SINGLE HOP

• MULTIHOP

• F c = (N max)^ ½

Fc CRITICAL FERQUENCY

N max MAXIMUM ELECTRON DENSITY

MODES OF PROPAGATION

EM SPECTRUM

• Electromagnetic waves has been classified into several ranges of frequencies

• Very low frequency (3 kHz to 30 kHz)

• Low frequency (30 kHz to 300 kHz)

• Medium frequency (300 kHz to 3000 kHz) & so on

• Even though the frequency range is very vast ; the propagation of these frequencies

through the free space can be grouped into 3 distinct modes:

1. The ground wave propagation

2. The sky wave propagation

3. The space wave propagation

1. Ground wave propagation

• Radio waves below 3 MHz which includes VLF, LF & MF – propagated through the surface of the earth

• This form of prop. Is “Ground wave propagation”

2.Sky wave propagation

• Freq.'s in the range of 3 MHz to 30 MHz – propagated through the ionosphere

• The propagation of these waves are said to be “sky wave propagation”

3.Space wave propagation

• At the freq.’s above 30 MHz – propagated through the troposphere

• These waves are called as “space waves” or “tropospheric” waves

• The propagation of these waves are said to be “space wave propagation”

MORE ABOUT SPACE WAVE PROPAGATION....

• LOS path

• Ground reflected path

Repeaters

DIVERSITY RECEPTION SCHEMES

(a) Frequency diversity technique

(b) Space diversity technique

(c) Polarization Diversity

• A single RF carrier is propagated with two different electromagnetic polarization

• This is achieved by using vertically & horizontally polarized antennas at the transmitter and receiver

• The idea is that EM waves of different polarization may not experience the same transmission degradation

• may be used with space diversity

Fig: Antenna Arrangement in space diversity reception

Multipath Interference

Fading

Four types of fading:

1. absorption fading2. reflection multipath fading3. atmospheric multipath fading and 4. sub-refraction fading

(b) Reflection multipath fading

(c) Atmospheric multipath fading

(d) Sub refraction fading

What is a Spot Beam?

• A spot beam is a satellite beam which is focused on a relatively small portion of the earths surface.

Uplinking Antenna

Satellite

IMD Server,Delhi

LAYOUT FOR DATABROADCAST

WORLD SPACE RECEIVER

DDA

128 Kbps

PC

PC

Remote Sites

INTERNET

OPTION-2

World Space Server,Singapore

(currently)

OPTION -1

Dedicated 64Kbps link

to be provided by VSNL

PC Card with built-in

Receiver &

DDA

64Kbps Local Leased line Connectivity

FACTORS AFFECTING MW LINK

Following major phenomenon affect MW Link

• 1.    REFLECTION

• 2.    REFRACTION

• 3.    DIFFRACTION

• 4.    SCATTERING

• 5.    ABSORPTION

Terrestrial Microwave Antennas

The principle of troposcatter radio communications

Optical and Radio Horizons

Fig: Effect of atmospheric refraction

THANK YOU