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
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Mw day 1
1. EC04 - 702:
MICROWAVE DEVICES AND COMMUNICATION
By
AJAL.AJ
Faculty , Dept of ECE
METS SCHOOL OF ENGINEERING,MALA
2. 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.
3. 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
4. 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)
5. 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
6. 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 access
schemes - digital satellite links
37. 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
38. 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 klystron
2) Twystron hybrid amplifier
39. SIGNAL SOURCES THAT
GENERATE POWER
Microwave tubes
@
Frequency > 1GHz
E.g.: klystron,
Traveling Wave
Tube, magnetron
conventional vacuum
tubes @
frequency < 1GHz
E.g. : triodes, tetrodes,
pentodes
40. What are all the constraints of
ordinary vacuum tubes at
frequencies beyond 1 GHz????
41. 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
42. Types of Microwave Tubes
Linear beam tubes
(O – Type)
Crossed Field Tubes
(M – Type)
Eg:
Klystron
Reflex klystron
TWT
Eg:
Magnetron
43. 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
44. Types of Linear Beam Tubes
TWYSTRON
MULTI
CAVITY
KLYST
TWO
CAVITY
KLYST
LINEAR BEAM TUBES
KLYSTRON
TUBES
HYBRID
TUBES
TRAVELING
WAVE TUBES
REFLEX
KLYST
LADDE-
RTRON
HELIX RING-
BAR TWT
COUPLED
CAVITY
TWT
HELIX
BWO
45. TWYSTRON
• KLYSTRON + TWT = TWYSTRON
• It is hybrid amplifier that uses the
combinations of klystron and TWT
components
46.
47.
48. 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
106. • Because of negative resistance in the
forward characteristics, the device can
be used actively as an oscillator
• Tunnel diode symbol
107. - Ve Resistance Region
VfVp
Ip
Vv
Forward Voltage
Reverse voltage
Iv
Reverse
Current
ForwardCurrent
Ip:- Peak Current; Iv :- Valley Current; Vp:- Peak Voltage
Vv:- Valley Voltage; Vf:- Peak Forward Voltage
I V - CHARACTERISTIC OF TUNNEL DIODE
p
V
109. • 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
116. 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
126. History
transit-time delay 에 의한 negative differential resistance 를
는 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)
127. Structure
P-n junction, Schottky barrier, or 이 둘
의 조합으로
Doping level : 0.5~10um
Substrate 는 low series resistance 때문
에 변질됨
Series resistance 로부터 power
dissipation 을 줄이기 위해서 가끔
substrate 는 10um 보다 두꺼워 짐
130. Characteristic
전압이 depletion edge meet 까지 가
면 , punch-through 가 일어남
Junction 이 asymmetrical 하면 ,
Vpt≠V‘
pt
이러한 characteristic 은 negative
differential resistance or negative
dV/dI 에서는 일어나지 않음
131. Characteristic
Punch-through 에서 전압
Flat-band condition 에서 전압
V1= injecting junction 을 지나는
공급된 전압의 일부
Injection current
s
biD
s
D
pt
qN
L
LqN
V
εε
Ψ
−≈
2
2
2
s
D
FB
LqN
V
ε2
2
≈
( )
FB
FB
Ibi
V
VV
V
4
2
−
=−Ψ
4
)(
expexp*
1exp
)(
exp*
2
2
2
−
−
≈
−
Ψ+
−=
FB
FBbp
p
Ibibp
pp
kTV
VVq
kT
q
TA
kT
qV
kT
q
TAJ
φ
φ
132. Characteristic
Charge Q 가 주어진 후에 ,
saturation velocity 로
substrate 를 돌아다님
Terminal current
Frequency
L
Qv
I sat
=
L
v
f sat
4
3
=
satv
134. 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
135. Related Device
1) Double-Velocity Transit-Time diode
(DOVETT)
• 유일한 특징은 saturation velocity
두 가지 값을 가진다는 것
• Heterojunction
• Injection current
- thermionic emission, tunneling
136. 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 : 1019
cm-3
, thickness : 10nm
• 장점 – high frequency capability (1000GHz), low voltage (2V)
137. Related Device
3) Quantum-Well-Injection Transit-Time Diode
(QWITT)
• Injection current – tunneling
• Higher frequency (TUNNETT)
• negative differential resistance
Resonant tunneling mechanism
139. MODULE 4
• IT’S ALL ABOUT TWO
COMMUNICATION SYSTEMS:
1. TERRESTRIAL MICROWAVE
COMMUNICATION SYSTEM
2. SATELLITE MICROWAVE
COMMUNICATION SYSTEM
140. 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
141. 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
148. 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
149. • 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
150. 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”
151. 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”
152. 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”
153. MORE ABOUT SPACE WAVE
PROPAGATION....
• LOS path
• Ground reflected path
158. (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
166. What is a Spot Beam?
• A spot beam is a satellite beam which is
focused on a relatively small portion of the
earths surface.
167. 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
168.
169. FACTORS AFFECTING MW
LINK
Following major phenomenon affect MW
Link
• 1. REFLECTION
• 2. REFRACTION
• 3. DIFFRACTION
• 4. SCATTERING
• 5. ABSORPTION
다른점
- injection current 가 barrier 넘어로 thermionic emission을 통해야 한다는 점
- avalanche current와 같지 않게 BARITT diode injection current는 injection phase delay를 가지지 않음
Schottky-barrier injection에서 (a)는 under thermal equilibrium이고 (b)는 punch-through에서 이고, (c)는 flat –band condition에서의 상태를 나타낸 것이다.
Injection cycle에서 bias 는 Vpt와 Vfb사이이다.
P-n junction의 경우 Øbp=0
(a)는 trminal 전압 이고, (b)는 injection current이고, (c) terminal current 의 파형이다
라모 쇼클리 이론에 의하면 L부분에 위치한 두개의 일렉트로드에서 움직이는 charge 는 터미널 전류를 야기시킨다
전압이 계속 positive cycle이기 때문에 이 부분에서 전류의 일부는 dissipative하다. 이것이 IMPATT diode 와 비교해 BARITT diode의 reduced efficiency가 더 많이 감소되는 이유이다
Maximum efficiency는 BARITT diode에서 10%, IMPATT diode 에서는 15%이다
Terminal current pulse width는 transit time에 의해 결정 된다, 그리고 그것은 ¾ cycle이다
BARITT의 파워 프리퀀시 특징에 대해 나타낸 표이다.
파워는 f의 제곱에 비례하여 감소한다
IMPATT와 관련이 있는 에벌런치 전류는 노이즈가 많고, 75~150V나 되는 높은 전압을 필요로 함
펀치 뜨루 다이오드는 지너 다이오드 우개를 back to back 로 연결해서 대체 할 수도 있음음
이것의 유일한 특징은 나뉘어져 있다는 것이다.
Heterojunction 에 의해 saturation velocity가 달라진다.
(a)는 structure이고, (b)는 피엔 정션 인젝터에서 밴드 투 밴드 터널링 에너지 밴드 diagram이고, (c) 는 쇼트키 배리어 인젝터에서 배리어를 통한 터널링 에너지 밴드 diagram이다.
(a)는 structure이고, (b)는 에너지 밴드 diagram이고, (c) 는 레조넌트 터널 다이오드 인젝터의 아이브이 특성.
8장에서 보았던