mw day 1
DESCRIPTION
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 klystron 2) Twystron hybrid amplifier CYLINDRICAL LINEAR COAXIAL VOLTAGE-TUNABLE INVERTED COAXIAL FREQUENCY-AGILE COAXIALTRANSCRIPT
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