Antenna and Microwave Engineering MCQs with answers Page - 11

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Q. The frequency of oscillation in Gunn diode is given by:

• (A) vdom/ leff
• (B) leff/ vdom
• (C) leff/ wvdom
• (D) none of the mentioned

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Correct answer - Option (A)

Explanation:

in gunn oscillation mode, the frequency of oscillation is given by vdom/ leff, where vdom is the domain velocity, leff is effective length that the domain moves from the time it is formed until the time a new domain is formed.

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Q. In Gunn diode oscillator, the Gunn diode is inserted into a waveguide cavity formed by a short circuit termination at one end

• (A) true
• (B) false
• (C) ---
• (D) ---

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Correct answer - Option (A)

Explanation:

the gunn diode is mounted at the centre of the broad wall of a shorted waveguide since for the dominant te10 mode; the electric field is maximum at the centre.

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Q. In a Gunn diode oscillator, the electron drift velocity was found to be 107 cm/second and the effective length is 20 microns, then the intrinsic frequency is:

• (A) 5 ghz
• (B) 6 ghz
• (C) 4 ghz
• (D) 2 ghz

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Correct answer - Option (A)

Explanation:

the intrinsic frequency for a gunn oscillator is given by vd/l. here vd is the drift velocity and l is the effective length. substituting the given values in the above equation, intrinsic frequency is 5 ghz.

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Q. The material used to fabricate IMPATT diodes is GaAs since they have the highest efficiency in all aspects.

• (A) true
• (B) false
• (C) ---
• (D) ---

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Correct answer - Option (B)

Explanation:

impatt diodes can be fabricated using silicon, germanium, gaas or indium phosphide. out of these materials, gaas have highest efficiency, low noise and high operating frequencies. but gaas has a major disadvantage of complex fabrication process and higher cost. so, gaas are not preferred over silicon and germanium.

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Q. 3 IMPATT DIODES, SCHOTTKY BARRIER DIODES, PIN DIODES

• (A) avalanche multiplication
• (B) break down of depletion region
• (C) high reverse saturation current
• (D) none of the mentioned

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Correct answer - Option (A)

Explanation:

a reverse bias voltage exceeding the breakdown voltage is applied to an impatt diode, a high electric field appears across the n+ p junction. this high field imparts sufficient energy to the holes and also to valence electrons to raise themselves to the conduction band. this results in avalanche multiplication of electron hole pair.

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Q. To prevent an IMPATT diode from burning, a constant bias source is used to maintain at safe limit.

• (A) average current
• (B) average voltage
• (C) average bias voltage
• (D) average resistance

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Correct answer - Option (A)

Explanation:

avalanche multiplication is a cumulative process resulting in rapid increase of carrier density. to prevent the diode from burning due to this increased carrier density, a constant bias source is used to maintain average current at safe limit.

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Q. The number of semiconductor layers in IMPATT diode is:

• (A) two
• (B) three
• (C) four
• (D) none of the mentioned

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Correct answer - Option (C)

Explanation:

impatt diode consists of 4 layers according to the construction. it consists of a p+ region and n+ layers at the two ends. in between these layers, a p type layer and an intrinsic region is sandwiched.

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Q. The resonant frequency of an IMPATT diode is given by:

• (A) vd/2l
• (B) vd/l
• (C) vd/2πl
• (D) vdd/4πl

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Correct answer - Option (A)

Explanation:

the resonant frequency of an impatt diode is given by the expression vd/2l. here vd is the carrier drift velocity; l is the length of the intrinsic region in the impatt diode.

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Q. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the drift time of the carrier is:

• (A) 10-11 seconds
• (B) 2×10-11 seconds
• (C) 2.5×10-11 seconds
• (D) none of the mentioned

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Correct answer - Option (B)

Explanation:

the drift time of the carrier is defined as the ratio of length of the intrinsic region to the carrier drift velocity.

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Q. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the nominal frequency of the diode is:

• (A) 12 ghz
• (B) 25 ghz
• (C) 30 ghz
• (D) 24 ghz

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Correct answer - Option (B)

Explanation:

nominal frequency is defined as the ratio of the carrier drift velocity to twice the length of the intrinsic region.

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