Antenna and Microwave Engineering MCQs with answers Page - 1

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Q. The major drawback of frequency multipliers is that they have:

• (A) higher attenuation
• (B) complex construction methods
• (C) complex design
• (D) none of the mentioned

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Correct answer - Option (C)

Explanation:

designing a good quality frequency multiplier is more difficult since it non-linear analysis, matching at multiple frequencies, stability analysis and thermal considerations. considering all these issues for designing a multiplier makes it very complex.

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Q. Oscillators operating at millimeter wavelength are difficult to realize and are also less efficient.

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

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Correct answer - Option (A)

Explanation:

as frequency increases to the millimeter wave range, it becomes increasingly difficult to build fundamental frequency oscillators with good power, stability and noise characteristics. an alternative approach is to produce a harmonic of a low frequency oscillator through the use of frequency multiplier.

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Q. A major disadvantage of frequency multipliers is that they multiply the noise factor along with frequency.

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

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Correct answer - Option (A)

Explanation:

a disadvantage of frequency multipliers is that noise levels are also increased by the multiplication factor.

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Q. If a frequency multiplier has a multiplication factor of 10, then the increase in noise level due to frequency multiplication is:

• (A) 10 db
• (B) 20 db
• (C) 25 db
• (D) 15 db

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Correct answer - Option (B)

Explanation:

for a frequency multiplier, the increase in noise power is given by 20 log n, where n is the multiplication factor of the multiplier. substituting in the below equation, increase in noise level is 20 db.

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Q. In a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with at all frequencies other than required harmonic.

• (A) real impedances
• (B) reactive impedance
• (C) complex impedance
• (D) none of the mentioned

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Correct answer - Option (B)

Explanation:

in a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with reactive impedance at all frequencies other than required harmonic nfo. if the diode junction capacitance has a square –law i-v characteristic , it is necessary to terminate unwanted harmonics with short circuit.

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Q. Resistive multipliers are more efficient as compared to reactive multipliers.

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

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Correct answer - Option (B)

Explanation:

resistive multipliers generally use forward biased schottky-barrier diodes to provide non linear characteristic. resistive multipliers have low efficiency but have better bandwidth.

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Q. Reactive multipliers have a disadvantage that they cannot be used at very high frequencies and they become less efficient.

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

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Correct answer - Option (A)

Explanation:

at millimeter frequencies, varactor diode exhibits resistive property. hence, at high frequency the multiplier becomes lossy and also does not offer high bandwidth, which is a major disadvantage.

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Q. For a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is:

• (A) 50 %
• (B) 25 %
• (C) 75 %
• (D) 12.5 %

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Correct answer - Option (B)

Explanation:

for a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is given by 1/m2 where m is the multiplication factor. for a factor 2 multiplier, maximum theoretical conversion efficiency is 25 %.

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Q. is a device that converts electrons to photons or vice-versa.

• (A) antenna
• (B) electron gun
• (C) photon amplifier
• (D) microwave tube

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Correct answer - Option (A)

Explanation:

antenna is a device that converts electrons into photons or vice versa. a transmitting antenna converts electrons into photons while a receiving antenna converts photons into electrons.

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Q. The basic equation of radiation that is applied to any antenna irrespective of the type of the antenna is:

• (A) il= qv
• (B) iq = lv
• (C) i/l=q/v
• (D) none of the mentioned

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Correct answer - Option (A)

Explanation:

basic equation of radiation is given by il=qv. i is the time change in current, l is the length of the current element, q is the charge v is the acceleration of the charge.

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