Download Historical evolution of Microwave Sources

Solid
State Microwave
Devices
Present State of Development
& Future Projections
1
Historical evolution of
Microwave Sources
1.Microwave is the region after
radio waves.
2.Radio waves are meant for
communication.
3.When a very long distance
communication was requiredthese waves failed to provide the
required characteristics and the
need for microwaves was felt.
2
 What
are Microwaves ?
3
What are Microwaves?
These are Electromagnetic (EM) Waves
having Frequency in the
Microwave Regions
Although there is no clear cut,
cut off frequency for the start or end
of the Microwave Regions
But
EM waves lying in the frequency region
of
1 GHz  f  300 GHz
are termed as Microwaves
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Frequency
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loi
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Ga Cos
mm mic
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a
Free space wavelength
Spectrum of Electro Magnetic Waves (EMW)
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Basic Production Mechanism of
Microwaves
Any Charge Particle which is either
– De-Accelerating or
– Oscillating or
– Pulsating
Produces Electromagnetic Waves
More the energy of this particle,
higher will be the Frequency as well as
Energy of the Radiations produced
E particle = h f
if this f, falls in Microwave bands, we get
Microwaves
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• The Charged particle with the
smallest mass is ELECTRON
• Therefore, whenever a beam of
High Energy Electrons is allowed to
•
De-Accelerate or
•
Oscillate or
•
Pulsate
• Microwaves are produced
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DEVICES (tool) FOR
THE PRODUCTION OF
MICROWAVES.
8
There are two types of Microwave
Sources
1. Vacuum Tube based
2. Solid State based
They are further classified as
1. Pulsed Power Sources
2. CW Power Sources
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Vacuum Tube based
 Vacuum
based tube were
insensitive to temperature.
 Did not get affected by
radiation .
 However the demerits marked
more.
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MICROWAVE PRODUCTION
USING VACUUM TUBES



Initially thorium plated cathode was
used to make work function lower.
It emitted electrons and anode
collected it (grid).
This was the simple concept of
generating frequency.
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How any frequency gets
generated?
.As any energy is given to electrons they
reach a higher energy level.
.They however want to come back to
there original level.
.During the process of coming back they
emit radiation
E=hv
v=frequency
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 IT
DEPENDS ON WHAT IS
THE LEVEL AT WHICH
ELECTRONS ARE PLACED
SO THAT WHEN SPECIFIC
ENERGY IS APPLIED THEY
EMIT A PARTICULAR
FREQUENCY.
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CEI 901-1 Receiver
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901-1 top inside
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7077 ceramic planar triode is
about the size of a kidney bean.
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Early '20 S tube
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Early '10 rectifier
tube
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Transmitter Power tubes circa 1925, the
largest glass RF power tubes still using
forced air cooling system
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Transmitter Power tubes circa 1925, the improveddesign second largest glass RF power tubes with large
anode(plate) contact outside for water cooling system
which can dissipate more power
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Late '20 ST tube
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Transmitter tube in '30
era
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Transmitter tube in '40
era
The smallest vacuum
tube(invented by RCA in 1959)
MICROWAVE TUBES
OSCILLATORS
AMPLIFIERS
1)REFLEX KLYSTRON
2)MAGNETRON
1)KLYSTRON
2)TRAVELLING WAVE
TUBES-TWT
Linear Bunching / Time Bunching of
Electron Beam Pulses
Electron Beam Pulses
.modulate the velocity of
electron beam
. these velocity-modulating
electron beam
releases their magnifying energy
in last cavity
and transfer it
into magnifying RF of same frequency
Electron Beam
Pulses
Bunching of
Electron Beam
Pulses
Basics of Azimuthal Bunching
Phase Bunching/Azimuthal Bunching/Angular
Bunching: wc = (e/m)×()
early 1940s Pierce and Shepherd of Bell Lab
invented the reflex Klystron, which is low-power
device and used in the heterodyne oscillator of
radar receiver

.
Reflex Klystron
Present Status of Klystrons
1. 100 MW, 10 GHz, 2 µsec
2. 65 MW, 3.5 µsec
3. 200 MW, 1 µsec
The ultimate goal is to have
500 MW, 2 µsec
Klystrons
Relativistic Klystron
1. 5 MeV, 2 kA, 1 GW
2. 50 MeV, 20 kA, 1 TW
A 6 MW (peak) Klystron
In 1959 both Philco and SONY
introduced their transistorized
portable black-and-white TV.
Starting from 1952 UHF TV emerged,
all UHF TV transmitter used
Klystron amplifier.
Vidicon and
Photomultiplier
Vacuum Tube based Devices
Present Scenario:
Triodes, Tetrodes, Pentodes
Klystrons
Relativistic Klystrons
Travelling Wave Tubes
Magnetrons
Future Scenario: Gyroklystrons
Gyrotrons
Lasertrons
Microlasertrons
Gigatron
Thyratron and Ignitron
In 1921 Hull of GE proposed magnetron
, in 1935 Ponte and Gotten of CSF
invented the magnetron
and later in 1940 Randall
and Boot of Univ. of Birmingham
independantly also invented Magnetron
Magnetron---first microwave
power oscillator



uses multiple resonant cavities in a
electron tube
exerting a strong orthogonal magnetic
field
can generate microwave energy at
3GHz around 1 kw at that time
Magnetron: Microwave Oscillator
A cutaway View of the Magnetron
An Inner View of a Magnetron
250 kW, 5 – 6 GHz
400 kW, 10 GHz
at least 10 times
frequency ability
than triode or tetrode
transmitting tubes
at that time.
Soon the magnetron developed very fast
due to high demand of war radar .
For example Western Electric
manufactured
10,000 units per month of X-band
magnetron
in early 1944 for bomber.
TWT ( Travelling Wave
Tube)


In1944 Kompfner invented
TWT(Travelling Wave Tube)--Similar principle to Klystron but using
slow-wave structure instead

of resonant cavity
Has wider bandwidth but a little lower
efficiency
Traveling Wave Tube
Traveling Wave Tube
A Product of Toshiba Electron Inc.
transistors, germanium
power diodes -50’s era
Epoxy planar silicon transistors---most
popular silicon transistors in '60 era
Silicon power transistors
Integrated Circuits in '60
and '70 era
"Pancake" and other silicon
VHF~Microwave transistors
two different germanium
transistors---popular in '50 era
Transmitter tube popular
in '50 era

In 1937 Varian brothers invented
Klystron---first UHF and microwave
tube, which uses two or more
resonant cavities inside an electron
tube letting accelerated electron beam
passing through it.
AVALANCHE DEVICES
AND CIRCUITS
THESE ARE NEGATIVE RESISTANCE
DEVICES LIKETUNNEL DIODES
GUNN DIODES
THEY WORK ON THE PRINCIPLE OF
VOLTAGE BREAKDOWN ACROSS
REVERSE BIASED JUNCTION.

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THESE ARE JUNCTION
BASED DEVICES.



IN THESE DEVICES AN AVALANCHE IS
PRODUCED.
THE BREAKDOWN OF AVALANCHE
PRODUCES A HUGE SUPPLY OF
ELECTRON AND HOLE PAIR.
THEY DELIVER POWER BY
CONVERTING DC BIAS POWER INTO
MICROWAVES.
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READ DIODES





THEORY OF THE DEVICE WAS FIRST
GIVEN BY READ IN 1958.
THE DEVICE WAS BUILT BY LEE AND
HIS CO- WORKERS IN 1965.
READ DIODE WORKS IN TWO
DISTINCT MODES
1)IMPATT DIODES(5-10%EFF)
2)TRAPATT MODE(20-60%EFF)
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NEGATIVE RESISTANCE

THE CARRIERS DRIFT IN THE HIGH
FIELD REGION TO INDUCE AN
ELECTRIC CURRENT IN THE
CIRCUIT,WHICH IS 180 DEGREES
OUT OF PHASE W.R.T. APPLIED AC
VOLTAGE HENCE A
NEGATIVE RESISTANCE
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IMPATT DIODES


IMPACT IONIZATION AND TRANSIT
TIME DEVICES
THESE ARE READ DIODES THAT
EXHIBIT NEGATIVE RESISTANCE.
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NEGATIVE RESISTANCE
IS DUE TO



1) IMPACT IONIZATION AVALANCHE.
2) TRANSIT TIME TAKEN WHILE
DRIFTING THROUGH THE REGION.
CAME INTO EXISTENCE IN 1965.
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MATERIAL DOPING WISE:
(3 TYPES)



1) ABRUPT P-N JUNCTION
2) LINEARLY GRADED P-N JUNCTION
3) P-I-N JUNCTION
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WELL DESIGNED IMPATT
SHOULD HAVE:



APPROPRIATE IMPEDANCE OVER A
BROAD RANGE OF FREQUENCIES
IT SHOULD HAVE HIGH IMPEDANCE
FOR FREQUENCY LYING BETWEEN
DC-500MHZ
LOW IMPEDANCE AT OPERATING
FREQUENCIES.
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DIODE IS PUT IN
AMICROWAVE CAVITY
AND IS REVERSE BIASED

THE IMPEDANCE OF CAVITYINDUCTIVE
THE IMPEDANCE OF CAVITYCAPACITIVE
LEADS TO A RESONANT CIRCUIT

FREQUENCIES OF AROUND 100GHZ


ARE EASILY ATTAINABLE.
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TRAPATT DIODES
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