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  • Question

  • Consider the following statements

    1. Impedance of Gunn diode is about tens of ohms.
    2. Impedance of Impatt diode is a few ohms.
    3. Impedance of Impatt diode are of the same order.
    4. Impedance of Impatt diode is more than that of Gunn diode.
    Which of the above statement are correct?


  • Options
  • A. all
  • B. 1 and 2 only
  • C. 1, 2 and 3
  • D. 1, 2 and 4

  • Correct Answer
  • 1 and 2 only 

    Explanation
    A Gunn diode uses GaAs which has a negative differential mobility, i.e., a decrease in carrier velocity with increase in electric field.

    This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.

    A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.

    Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.

    An Impatt diode has n+ - p - i - p + structure and is used with reverse bias.

    It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit.

    The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode.

    The features of Impatt diode oscillator are : Frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%.

    Its applications include police radar systems, low power microwave transmitter etc.

    Microwave Communication problems

    Search Results

    • 1. Assertion (A): Magnetron is generally used in n mode.

      Reason (R): Frequency for p mode can be easily separated from adjacent modes.


    • Options
    • A. Both A and R are correct and R is correct explanation of A
    • B. Both A and R are correct but R is not correct explanation of A
    • C. A is correct but R is wrong
    • D. A is wrong but R is correct
      • Discuss
    • 2. To couple a coaxial line to a parallel wire line it is best to use

    • Options
    • A. slotted line
    • B. balun
    • C. directional coupler
    • D. ?/4 transformer
      • Discuss
    • 3. Assertion (A): The condition of minimum distortion in a transmission line is L = RC/G.

      Reason (R): Line loading means addition of inductance to satisfy the condition L = RC/G.


    • Options
    • A. Both A and R are correct and R is correct explanation of A
    • B. Both A and R are correct but R is not correct explanation of A
    • C. A is correct but R is wrong
    • D. A is wrong but R is correct
      • Discuss
    • 4. A (75 - J50) ohm load is connected to a coaxial of Z0 = 75 ohm at 10 GHz. The best method of matching is to connect

    • Options
    • A. an inductance at load
    • B. a short circuited stub at load
    • C. a short circuited stub at specific distance from load
    • D. a capacitance at specific distance from load
      • Discuss
    • 5. The total field developed by an antenna array at a distant point is

    • Options
    • A. phasor sum of fields produced by individual antennas of the array
    • B. algebraic sum of fields produced by individual antennas of the array
    • C. either (a) or (b) depending on type of array
    • D. neither (a) nor (b)
      • Discuss
    • 6. For a circular wave guide

    • Options
    • A. cutoff frequency for TE10 and TE01 modes are same
    • B. cutoff frequency for TE10 and TE01 modes are different
    • C. cutoff frequency for TE10 mode = twice the cutoff frequency for TE20 mode
    • D. cutoff frequency for TE10 mode = haf the cutoff frequency for TE20 mode
      • Discuss
    • 7. In a backward wave oscillator the wave

    • Options
    • A. travelling along the line winds itself back and forth
    • B. progresses only in forward direction
    • C. progresses only in backward direction
    • D. either (a) or (c)
      • Discuss
    • 8. If f is the frequency of electromagnetic wave, fc is cutoff frequency, then in a rectangular waveguide

    • Options
    • A. attenuation is low when f > fc
    • B. attenuation is low when f < fc
    • C. attenuation is high when f < fc
    • D. either (b) or (c)
      • Discuss
    • 9. In mode filter of the given figure which of the following modes is unaffected

    • Options
    • A. TE01
    • B. TE10
    • C. TE11
    • D. all TM
      • Discuss
    • 10. A branched duplexer requires

    • Options
    • A. TR tubes
    • B. ATR tube
    • C. both TR and ATR tube
    • D. none of the above
      • Discuss

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