66. The semiconductor diode which can be used in switching circuits at microwave range is:
    
    

1. 1. PIN diode
      

   
   
   

   2. Tunnel diode
      

   
   
   

   3. Varactor diode
      

   
   
   

   4. Gunn diode

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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67. Rain drop attenuation in most microwave communication links is caused due to:
    

1. 1. Scattering of microwaves by water drops of specific size
      

   
   
   

   2. Scattering of microwaves by a collection of droplets acting as a single body
      

   
   
   

   3. Absorption of microwave by water and consequent heating of the liquid
      

   
   
   

   4. Absorption of microwaves by water-vapour in the atmosphere

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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68. Which one of the following modes of transmission will not be supported by a rectangular waveguide?
    

1. 1. TE₁₀
      

   
   
   

   2. TM₁₁
      

   
   
   

   3. TE₁₁
      

   
   
   

   4. TM₁₀

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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69. In antenna measurements using two aperture antennas of dimensions D₁ and D₂, the minimum separation between the two should be (λ is the free-space wavelength of radiation used):
    

1. 1. (D1 + D2)/(2λ)
      

   
   
   

   2. (D1² + D2²)/(8λ)
      

   
   
   

   3. (D1² + D2²)/(λ)
      

   
   
   

   4. (D1²·D2 ²)/(2λ)

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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70. In both the sequential-lobing and conical-scan tracking techniques of radar, the measurements of angular errors in two orthogonal coordinates (azimuth and elevation) require that a minimum of:
    

1. 1. Three pulses be processed
      

   
   
   

   2. Two pulses be processed
      

   
   
   

   3. Four pulses be processed
      

   
   
   

   4. Only one pulse be processed

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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