120. Waveguides are used mainly for microwave signals because
A. they depend on straight-line propagation which applies to microwaves only
B. losses would be too heavy at lower frequencies
C. there are no generators powerful enough to excite them at lowe frequencies
D. the would be too bulky at lower frequencies

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121. A rectangular waveguide 2.29cm x 1.02 cm operates at a frequency of 11 GHz in TElo mode. If the maximum potential gradient of thesignal is 5 kV/cm, then the maximum power handling capacity of the waveguide will be
A.31.11mW
B.31.1IW
C.31.11 kW
D.31.11 MW

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122. A cavity resonator can be represented by
A. an LC circuit
B. an LCR circuit
C. a lossy inductor
D. a lossy capacitor

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123. The cut-off wavelength Xc for TE20 mode for a standdrd rectangular waveguide is
A. 2/a
B. 2a
C. a
D. 2a2

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124. In an air line, adjacent maxima are found at 12.5 cm and 37.5 cm. The operating frequency is
A. 1.5 GHz
B. 600 MHz
C. 300 MHz
D. 1.2 GHz

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125. The degenerate modes in a waveguide are characterised by
A. same cut-off frequencies but different field distributions
B. same cut-off frequencies and same field distributions
C. different cut-off frequencies but same field distributions
D. different cut-off frequencies and different field distributions

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126. For TM waves in a parallel plate waveguide, the minimum attenuation arising from imperfect conductors would occur at a frequency of (fc is the cut-off frequency)
A. 3fc
B.fc
C. 2fc
D.fc

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