ANTENNA AND MICROWAVE ENGG

A traveling-wave tube (TWT) amplifies by virtue of

• The absorption of energy by the signal from an electron stream

• The effect of an external magnetic field

• . The energy contained the cavity resonators

• The energy liberated form the collector

Oscillators of a klystron tube are maintained

• By bunches of electrons passing the cavity grids  

• By plate-to-cathode feedback

• By feedback between the accelerating grid and the repeller

• By circulating bunches of electrons within the cavities.

The coarse frequency adjustment of a reflex klystron is accomplished by

• The AFC system

• Adjusting the flexible wall of the resonant cavity

• An adjustment in the synchronizer

• Varying the repeller voltage

A reflex klystron is oscillating at the frequency of its resonant cavity. If the reflector voltage is made slightly less negative, the 

• Oscillation will cease

• Output power would increase

• The frequency will decrease

• Bunching would occur earlier in time

The maximum usable range of the usual radar set (on any particular range setting) is determined by 

• The width of the transmitted pulses

• The interval between transmitted pulses

• The bandwidth of the receiver IF stages

• The duty cycle

The main difference between the operation of transmission liners and waveguides is that 

• the latter is not distributed, like transmission lines

• the former can use stubs and quarter-wave transformers, unlike the latter

• transmission lines use the principal mode of propagation, and therefore do not suffer from low frequency cut-off

• terms such as impedance matching and standing-wave ratio cannot be applied to waveguides

Waveguides are used mainly for microwave signals because  a)  b)  c)  d)

• they depend on straight-line propagation which applies to microwaves only

• losses would be too heavy at lower frequencies

• there are no generators powerful enough to excite them at lower frequencies

• they would be too bulky at lower frequencies

When electromagnetic waves are propagated in a waveguide 

• they travel along the broader walls of the guide

• they are reflected from the walls but do not travel along them

• they travel through the dielectric without the walls

• they travel along all four walls of the waveguide

A microwave tube amplifier uses an axial magnetic field and a radial electric field. This is the 

• reflex klystron

• coaxial magnetron

• traveling-wave magnetron

• CFA

. High-power TWTs are replacing what in microwave amplifiers? 

• MESFETs

• Magnetrons

• Klystrons

• IMPATT diodes