Microwave Devices Final Lectures b

MICROWAVE DEVICES

IRINEO P. QUINTOECE / REE

MICROWAVE TUBES

• KLYSTRON AMPLIFIER– AMPLIFIES

MICROWAVE SIGNAL USING VELOCITY MODULATION

– FORMS HIGH VELOCITY ELECTRONS

– TYPICAL EFFICIENCY: 30-45%; MAX=70%

– 0.5 – 6.4 GHz

BUNCHER CAVITY CATCHER CAVITY

DRIFT SPACE

MICROWAVE TUBES

• REFLEX KLYSTRON– LOW POWER, LOW

EFFICIENCY MICROWAVE OSCILLATOR

– 4-200 GHz– <10% EFFICIENCY– TYP Po=100 mW

T = n + 3/4

T – transit time

n – any integer

REPELLER

OUTPUT

ANODE

MAGNETRON• A DIODE WHICH USES THE

INTERACTION OF MAGNETIC AND ELECTRIC FIELDS IN A COMPLEX CAVITY TO PROVIDE OSCILLATIONS

• 10 MW – UHF; 2MW – X-BAND; 80 kW – 95 GHz

• EFFICIENCY OF 50-60%

• TYPES OF:– HOLE & SLOT– VANE– RISING SUN– COAXIAL

MICROWAVE TUBES

• TRAVELING WAVE TUBE (TWT)– THE INTERACTION BETWEEN THE BEAM

AND THE RF FIELD IS CONTINUOUS– CAN BE USED AS A LOW-LEVEL, LOW

NOISE AMPLIFIER OR AS A HIGH POWER ONE, EITHER CW OR PULSED

– 2 – 16 GHz, 30-45 dB GAIN, F=4-10 dB, 10-100 mW

– CW 1-100 GHz, UP TO 10 kW, 25-35% effy

– PULSED 2-40 GHz,1-250 kW

• CROSS FIELD AMPLIFIER (CFA)– CROSS BETWEEN THE TWT &

MAGNETRON– PULSED TYPE 1-18 GHz, 5MW –

UHF, 70%; 1 MW – X BAND, 55%• BACKWARD WAVE OSCILLATOR

(BWO)– SHORTER & THICKER TWT– MICROWAVE CW OSCILLATOR– 1-1000 GHz

Microwave Tubes

1 MW

1 KW

1W

1mW

0.3 1 3 10 30 100 300 Frequency (GHz)

Av

era

ge

po

wer

Microwave tubes

Microwave semiconductor

devices

• Lower weight

• Smaller size

• Longer life time

• Higher power

• Limited life time

• High vacuum

• High potential

Two possible methods of achieving high output power in microwave system

Low power semiconductor

oscillator

High power tube amplifier

High power tube

oscillator

Important Parameters • Peak power • Average power• Efficiency • Gain • Bandwidth • Frequency • Harmonic and spurious power • Intermodulation products • Manufacturability at low cost

TypeRelative BW (%)

(%)Gain (dB)

Relative spurious

level

Relative operating

voltage

Relative complexity

of operation

Gridded tube 1-10 20-50 6-15 2 Low 1

Klystron 1-5 30-70 40-60 1 High 2

Helix tube 30-120 20-40 30-50 3 High 3

Coupled cavity tube

5-40 20-40 30-50 3 High 3

10 MW

1 MW

100 KW

10 KW

1 KW

100 W

0.3 1 3 10 30 100 300 Frequency (GHz)

Average power

Klystron

Coupled cavity TWT

Helix TWT

Gridded tube

1000 MW

100 MW

10 MW

1 MW

100 KW

10 K W

0.3 1 3 10 30 100 300 Frequency

(GHz)

Peak power

Coupled cavity TWT

Klystron

Gridded tube

Helix TWT

Klystron

Electron beam

Electron Gun

Intermediate cavity

Beam collector

Microwave input

Microwave output

TWT

Major applications for TWTs include:Amplifiers:• Space applications• Radar • Electron Counter Measure • Missile

Driver for other high power RF amplifiers

Missile TWTs for Active Seekers

Features that influence the design include:

• Minimal size and weight;

• Narrow-to-moderate bandwidths;.

• Off-to-fully-operational turn-on times of one second or less;

• High efficiency;

• High reliability after long inactive storage periods.

Normally, these TWTs are of the periodic-permanent-magnet (PPM) focused helix variety. They normally utilize unique cathode-heater designs to provide the very fast warm-up required. They typically have multiple stage depressed collectors with conduction cooling.

Microwave Ovens

5. Microwave ovens

Source:NPL

Electromagnetic spectrum

• Microwaves• From

– 0.8 GHzto

– 1000 GHz

1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022

Radio & TVInfra Red

Microwaves

Gamma-Rays

X-Rays

Ultra Violet

Microwaves

Conventional Oven

Microwave Oven

Absorption (1)Too strong

• If power were absorbed too strongly,– Microwaves would only penetrate a short distance– Surface would be heated– Inside would remain uncooked

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.01 0.1 1 10 100

Lo

ss o

f en

erg

y in

wa

ter

at 0

C

Frequency (GHz)

Microwave ovens operate at 2.45 GHz

Absorption (2) Too weak

• If power were absorbed too weakly,– Microwaves would go right through – No cooking

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.01 0.1 1 10 100

Lo

ss o

f en

erg

y in

wa

ter

at 0

C

Frequency (GHz)


Absorption (3)

• If power is absorbed just right,– Microwaves penetrate about 5 cm (2 inches) – Cooks the outer 5 cm of the food– Good enough for most cases

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.01 0.1 1 10 100

Lo

ss o

f en

erg

y in

wa

ter

at 0

C

Frequency (GHz)


Microwave OvensSummary

• A microwave oven cooks food by heating it• The heating comes from

– intense waves at 2.45 GHz • rather than

– a wide spectrum of waves at infra red frequencies.– Frequency chosen because of absorption properties

of water molecules at that frequency.

Microwave GenerationCavity Magnetron Valve

Microwave Ovens

Magnetron

Microwave Ovens

Inside a microwave oven

Microwave Power

• Power– This is a 700 watt oven– Think of 7 x 100 watt light bulbs

MicrowaveElectric field

• 700 watts – Around 140 000 volts per metre– Look what happens to a CD

Microwave Intensity

• 700 watts – transmitted into an area of around 1/25th square metre– Between 104 to 105 watts per square metre– (Most intense sunlight around 103 watts per square metre)– Very Dangerous– Could I have a stupid volunteer please?

A Cautionary Tale

Don’t try this at home!

August 14, 2002 I don't want to sound like I know everything in the world or even like I know quite a lot. But you had a question regarding “If a microwave oven door were to open while it was still on, what would happen? Could it hurt you?- JP” Well ..Having the thought process that I have, kinda how should I put it? ...Stupid? or inventive or even in-between. Well, my microwave door did happen to come off. Magic Chef 900-watt microwave. Well, I did my best to try to fix it but the hinge on one side did not attach properly, therefore having a gap between the door and the appliance. Being me (stupid) I wondered if it would burn fast or would it gradually warm up. I slid my finger between...You probably dying to hear what happened... But it didn't gradually warm up at all. It was instant heat! It didn't scar me or anything like that, but sure scared the H*** out of me to find out it got so hot so quick. I didn't get any blisters either. But it just burned like touching something hot on the tip of my finger being that is the only thing I put in. Well you know the old adage, "You learn from your mistakes", stands true. lol -

Microwave OvenSAR inside oven

• Inside – 700 watts:– Absorbed in 1 kg of water: SAR = 700 watts per kg– Your brain weighs about a kilogram!

• QUESTION: After 1 minute, what temperature rise results from an SAR of 700 watts per kg?

Microwave Ovens (13) SAR

SAR Wattsper kilogram

Temperature Rise in 1 kg of ‘Brain Fluid’

Microwave 700 8 ºC (ish)

Mobile Phone 1 Can’t be measured directly

Expect 1/700 of microwave temperature riseThe effects of blood flow reduce this further

http://blog.earthshod.co.uk/wp-content/uploads/2008/12/micro1.png

http://blog.earthshod.co.uk/wp-content/uploads/2008/12/micro2.png

Semiconductor Microwave Devices

SEMICONDUCTOR MICROWAVE DEVICES

• TRANSISTOR– 2-4 GHz, 9W, 12-8 dB– 29.5-32.5 dB at 4-6 GHz, 15

mW– FET – G=10dB, 9-15 GHz, F=7-

14 dB• PARAMETRIC AMPLIFIER

– USES A DEVICE WHOSE REACTANCE VARIES SUCH THAT AMPLIFICATION RESULTS

• GUNN DIODE– WORKS ON THE PRINCIPLE OF

TRANSFERRED ELECTRON EFFECT

– MADE WITH GaAs AND InP– CW 4-75 GHz (1.5W – 50

mW), 12-2% (TYP EFFY: 2.5-5%)

SEMICONDUCTOR MICROWAVE DEVICES

• IMPACT AVALANCHE & TRANSIT TIME DIODE (IMPATT)

– MADE OF Si OR GaAs– WORKS LIKE TUNNEL DIODE / GUNN

DIODE– MADE OF 4 LAYERS

• TRAPPED PLASMA AVALANCHE TRIGERRED TRANSIT TIME DIODE (TRAPATT)– PULSED – 600 W, 1 GHz, 75%

(TYP:30%)

• OTHER MICROWAVE DIODES– TUNNEL– VARACTOR– SCHOTTKY BARRIER– PIN

Microwave Engineering/Active Microwave Devices 9-13 September 2006

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Semiconductor Microwave Devices

DeviceFrequency Limitation

Substrate Material

Major Applications

IMPATT < 300 GHz Si, GaAs, InP Transmitters Amplifiers

Gunn < 140 GHz GaAs, InPLocal oscillators, Amplifiers

Transmitters

FET&HEMT < 100 GHz GaAs, InPAmplifiers , Oscillators, Switches,

Mixers, and Phase shifters

p-i-n < 100 GHz Si, GaAsSwitches, Limiters, Phase shifters,

Modulators, and Attenuators

Varactor < 300 GHz GaAsMultipliers, Tuning, Phase shifters,

and Modulators

Most microwave devices are fabricated on a GaAs substrate because of its high mobility. A silicon substrate, on the other hand, has the advantages of low cost and high yield. The following table summarizes the various microwave solid-state devices and their applications.


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Microwave Diodes

Non-linear I-V Characteristics Non-linear C-V Characteristics

Frequency mixing Frequency multiplication

Harmonic generation Voltage Controlled Oscillator

Switching Voltage tuned filter

Modulation Frequency conversion

Limiting Harmonic generation

Detection Parametric amplification

A microwave diode is much more than just a two-element device which has limited capabilities. It is a complex device which an integral part of many sophisticated microwave systems. Many devices have been developed using the non-linear I-V and C-V characteristics of the p-n or Schottky-barrier junction. Various applications are summarized below


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Non-Linear Characteristics of p-n and Schottky diodes

V

I

IsVB

Non-linear I-V Characteristics of a diode

V

C

VB

Non-linear I-V Characteristics of a diode

Vbi


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Varactor Devices and Circuits

Semiconductor p-n junction, or Schottky-barrier

n-type semiconductors with p-type diffusion

Important parameters:

Q factor

Cutoff frequency

Breakdown voltage

Sensitivity.


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Applications:

(1) Voltage controlled Oscillator VCO:

FM systems and frequency agile systems

Instrumentation

Electronic warfare (EW)

Electronic counter measurement (ECM) systems.


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(2) Multiplier and harmonic generation

Feasible alternative for the generation of high frequency signal

Zo

Zo

LPF and matching

BPF and matching

Cj(V)

Rs Varactor


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(3) Parametric Amplifiers:

Provide very low noise amplification

Pump signal

Input

Output

CirculatorCombiner and

Varactor


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p-i-n Diodes

Similar to the pn diode with smaller junction capacitance

Very useful for a diode used a microwave switch

P+ n+i

Weakly doped f.b. r.b.

Rj(V) Cj(V)

Rp

Ls

Rs

P-i-n structure

Equivalent circuit of p-i-n

Parasitics Ls~ 0.1 nH Cp~ 0.3 pF Rs~ 0.3


42

Switches Applications

t

Switch

Bias

Source

Output

(1) Modulators in communication systems

.

.

.

Wideband switch

(2) Switch in wide band system


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(4) Channel selection in wideband system

(5) Signal path control in measurement systems

As a switch the main important p-i-n diode parameters are Isolation and Insertion loss

(3) To protect receiver from the transmitter (such as in radar system)

Rx

Tx


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p-i-n Diode Attenuator

p-i-n diode attenuator circuits are used extensively in automatic gain control (AGC) and RF leveling applications as well as in electronically controlled attenuators and modulators

Zo

Zo

A = 20log (1 + Zo/2Rs)

Reflective type


45

p-i-n diode

p-i-n diode

Zo

Zo

Bias

Input

Output

3-dB quadrature coupler

Matched attenuator


46

p-i-n Phase Shifters

3-dB, 90o

Hybrid

B2B1 B2B1

DiodeDiode

/4

Zo

Hybrid coupler phase shifter. Uses the fewest diodes. Any phase shift increment can be obtained with proper design of the terminating circuit.

The loaded line phase shifter

Input Output

Input Output


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Switched line phase shifter

L1

L2

Bias

Switching action is used to obtain insertion phase by providing alternative transmission paths, the difference in electrical length being the desired phase shift


48

Limiter p-i-n Diodes

Used for protection applications

3 dB Coupler

3 dB Coupler

Limiter

TransmitterReceiver

Limiter


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Pin

Pout

Insertion loss

Maximum Isolation

Pin Pout

p-i-n diode

Passive Limitation. No exterior control is needed and the incident microwave power is responsible for switching from the high impedance state to low impedance state of the diode


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Controlled limitations. A small part of the incident signal is sampled and detected by Schottky diode whose the rectified current biases the diode in the forward state. The losses at low level are slightly higher, adjustments are very difficult

Controlled limitations. This method gives lower losses, better isolation, but require a delicate control circuit. Any loose of control affect receiver protection

Pin Pout

Schottky diodep-i-n diode

Pin Pout

Control pulse

p-i-n diode


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Gunn DiodesSingle piece of GaAs or Inp and contains no junctions

Exhibits negative differential resistance

Applications:low-noise local oscillators for mixers (2 to 140 GHz). Low-power transmitters and wide band tunable sources

Continuous-wave (CW) power levels of up to several hundred mill watts can be obtained in the X-, Ku-, and Ka-bands. A power output of 30 mW can be achieved from commercially available devices at 94 GHz.

Higher power can be achieved by combining several devices in a power combiner.

Gunn oscillators exhibit very low dc-to-RF efficiency of 1 to 4%.


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Varactor Tuned Gunn Oscillators Circuits


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IMPATT Devices and Circuits

IMPact Ionization Transit Time

IMPATT devices can be used for oscillator and amplifier applicationsThey can be fabricated with Si, GaAs, and InP

Can be used up 400 GHz.

Noisy oscillator

In general, IMPATTs have 10 dB higher AM noise than that of Gunn diodes

IMPATT diode is not suitable for use as a local oscillator in a receiver.


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Some IMPATT Circuits

Documents

Microwave Devices Final Lectures b