Microwave Devices

MICROWAVE DEVICES IRINEO P. QUINTO ECE / REE

MICROWAVE TUBES 

KLYSTRON AMPLIFIER  AMPLIFIES MICROWAVE SIGNAL USING VELOCITY MODULATION  FORMS HIGH VELOCITY ELECTRONS  TYPICAL EFFICIENCY: 3045%; MAX=70%  0.5 – 6.4 GHz

BUNCHER CAVITY

CATCHER CAVITY

DRIFT SPACE

MICROWAVETUBES 

REFLEX KLYSTRON 

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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

OUTPUT REPELLER

ANODE

MICROWAVE TUBES 

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A DIODE WHICH USES THE INTERACTION OF MAGNET AND ELECTRIC FIELDS IN A COMPLEX CAVITY TO PROVIDE OSCILLATIONS 10 MW – UHF; 2MW – X-BAND; 80 Kw – 95 GHz EFFICIENCY OF 5060%

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TYPES OF:    

HOLE & SLOT VANE RISING SUN COAXIAL

MICROWAVE TUBES 

TRAVELING WAVE TUBE (TWT) 

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THE INTERACTION BETWEEN THE BEAM AND THE RF FIELD IS CONTINUOUS CAN BE USED AS A LOWLEVEL, 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

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CROSS FIELD AMPLIFIER (CFA) 

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CROSS BETWEEN THE TWT & MAGNETRON PULSED TYPE 1-18 GHz, 5MW – UHF, 70%; 1 MW – X BAND, 55%

BACKWARD WAVE OSCILLATOR (BWO) 

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SHORTER & THICKER TWT MICROWAVE CW OSCILLATOR 1-1000 GHz

SEMICONDUCTOR MICROWAVE DEVICES 

TRANSISTOR   

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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 SUCH THAT THE AMPLIFICATION RESULTS

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GUNN DIODE 

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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)  

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MADE OF Si OR GaAs WORKS LIKE TUNNEL DIODE

TRAPPED PLASMA AVALNCHE TRIGERRED TRANSIT TIME DIODE (TRAPATT) 

PULSED – 600 W, 1 GHz, 75% (TYP:30%)

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OTHER MICROWAVE DIODES    

TUNNEL VARACTOR SCHOTTKY BARRIER PIN

WAVEGUIDES 

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A HOLLOW METALLIC TUBE USED TO PROPAGATE SIGNALS TYPICALLY FROM 3100 GHz BAND TRANSMIS MULTIPLE SIGNAL OVER THE SAME FREQUENCY BUT IN DIFFERENT MODES

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ADVANTAGES 

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EASIER TO FABRICATE THAN COAXIAL LINE NO FLASHOVER BETTER POWER HANDLING CAPABILITY (10X AS MUCH AS COAXIAL LINE) LOWER POER LOSS HIGHER OPERATING FREQUENCY

BASIC TYPES OF WAVEGUIDES 

RECTANGULAR

MODES OF PROPAGATION TRANSVERSE ELECTRIC (TEmn) 0R H-MODE Zo = 120π / λo = 2 /

Vg = C sinθ Vp = C/sinθ VgVp = C2

1 – (λ/λo)2

(m/a)2 + (n/b)2

TRANSVERSE MAGNETIC (TM) 0R E-MODE Zo = 120π

1 – (λ/λo)2

DOMINANT MODE 

THE MODE YIELDING THE LONGEST CUT-OFF WAVELENGTH

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CIRCULAR WAVEGUIDE 

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TE10

& TM11 - RECTANGULAR

TE11

& TM01 - CIRCULAR 

Λo = 2πr / (KR) - CIRCULAR 

BIGGER CROSS SECTION THAN RECTANGULAR POSSIBILITY OF PLANE OF POLARIZATION TO ROTATE DUE TO DISCONTINUITIES OR ROUGHNESS EASIER TO MANUFACTURE THAN RECTANGULAR EASIER TO JOI TOGETHER

OTHER MICROWAVE DEVICES 

RIDGED WAVEGUIDE 

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SINGLE OR DOUBLE RIDGE TYPE LOWERS THE VALUE OF THE CUT-OFF WAVELENGTH, HENCE DECREASES THE GUIDE’S SIZE INCREASES THE USEFUL FREQUENCY RANGE REDUCE THE PHASE VELOCITY HIGHER LOSS THAN ORDINARY RECTANGULAE WAVEGUIDE

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FLEXILE WAVEGUIDES (ELLIPTICAL WAVEGUIDE)  

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MAYBE BENDED, TWISTED OR STRECTH DOES NOT REUIRE JOINS AND SEPARATE BENDS ALMOST THE SAME POWER HANDLING ABILITY, ATTENUATION AND SWR THAN RECTANGULAR

OTHER MICROWAVE DEVICES 

FLANGE 

USED TO JOIN WAVEGUIDES TOGETHER TO ENSURE A SMOOTH MECHANICAL JUNCTION (LOW LEAKAGE & REFLECTIONS)

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TAPER & TWIST SECTIONS 

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JOIN WAVEGUIDES WITH DIFFERENT DIMENSINS OR CROSS SECTIONAL SHAPES

JUNCTIONS   

H-PLANE T (SHUNT) E-PLANE T (SERIES) HYBRID / MAGIC T

OTHER MICROWAVE DEVICES 

MATCHING SECTIONS

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IRIS (CAPACITIVE / INDUCTIVE) TUNING SCREW 

APPEARS CAPACITIVE LESS THAN λ/4 AND INDUCTIVE IF MORE THAN λ/4

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SLIDE SCREW TUNER ATTENUATOR SLOTTED LINE SWR METER ISOLATOR 

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CIRCULATOR 

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MADE OF FERRITE SIMILAR TO ISOLATOR

POINT CONTACT DIODE 

USED AS MIXER/DETECTOR

PROBLEMS 

WHAT WILL BE THE CUTOFF WAVELENGTH FOR THE DOMINANT MODE IN RECTANGULAR WAVEGUIDE WHOSE BREADTH IS 10 cm? FOR A 2.5 GHz SIGNAL PROPAGATED IN THIS GUIDE IN THE DOMINANT MODE, CALCULATE THE UIDE WAVELENGTH, THE GROUP AND PHASE VELOCITIES AND THE CHARACTERISTIC WAVE IMPEDANCE?

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IT IS NECESSARY TO PROPAGATE A 10 GHz SIGANL IN A GUIDE WHOSE WALL SEPARATION IS 6 cm. WHAT IS THE GREATEST NUMBER OF HALFWAVES OF ELECTRIC FIELD INTENSITY WHICH IT WILL BE POSSIBLE TO ESTABLISH BETWEEN THE TWO WALLS?