Microwave Lab - Viva Questions

Microwave Lab Viva Questions With Answers

Familiarization of microwave components

1. List out the microwave frequency bands and corresponding frequency ranges.

λ nm	Loss (dB/km)
UHF	0.3 - 1.0
L	1.0 - 1.5
S	1.5 - 3.9
C	3.9 - 8.0
X	8.0 - 12.5
Ku	12.5 - 18
K	18 - 26

2. What are the applications of a magic tee?

(a) As a matching device

(b) As an isolator

(c) As a phase shifter

(d) As a transmit-receive switch in Radar.

3. What is the microwave frequency range ?

Roughly 1 GHz to 1000 GHz

4. What is the range of wavelength of micro wave frequency?

0.1 cm to 100 cm.

5. Which is the band of frequency used usually in laboratory experiments ?

X-band.

Frequency and wavelength measurements

6. What is the cut off wave length?

Cut off wavelength λ_c is defined as the smallest free space wavelength able to propagate through the waveguide with the given dimensions. 

7. What is the dominant mode of rectangular waveguide? Explain.

TE₁₀ is the dominant mode in a rectangular waveguide. TM_mn and TE_mn are the possible modes of propagations through the waveguides. In TM waves, m and n should be integers. If either m or n is zero, entire field will vanish. In the case of TE wave m or n can be made zero without causing all fields to vanish. Lowest frequency or longest wavelength is possible to propagate when m = 1 and n = 0. Hence TE₁₀ is the dominant mode.

8. What are m and n representing?

They represent the number of half period variation of the fields along x and y co-ordinates respectively.

9. How TEM waves are propagated?

TEM waves can be propagated by co-axial lines since it cannot be transmitted through the rectangular waveguides.

VSWR measurement:

10. Define reflection coefficient in terms of characteristic impedance and VSWR.

(Z – Z₀)/(Z + Z₀) = (S-1)/ (S+1)

 where Z is the impedance at a point on line, Zo is the characteristic impedance and S is VSWR.

11. What are the ideal values and range of reflection coefficient and VSWR ?

Ideally reflection coefficient is 0 and VSWR is 1. Range of reflection coefficient is 0 to 1 and that of VSWR is 1 to infinity.

12. What is the need of attenuator in the experimental set up?

To introduce desired attenuation so as to reduce the possibility of undesired frequency or amplitude changes in the source itself as a result of interaction of oscillator or probe.