Antennas and Microwave Engineering MCQ Questions with answers and solutions Page 17

Q. In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:

(A) 0.25 mhz
(B) 2.5 mhz
(C) 25 mhz
(D) 5 mhz

✅ Correct Answer: (A) 0.25 mhz

Explanation: the series resonant frequency of a crystal oscillator is given by 1/√lc. substituting the given values of l and c in the expression, the series resonant frequency is 0.25 mhz.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. Parallel resonant frequency of quartz crystal is given by:

(A) 1/ √(lcₒc/(cₒ+c))
(B) 1/√lc
(C) 1/√lcₒ
(D) 1/ √(l(cₒ+c) )

💬 Discuss

✅ Correct Answer: (A) 1/ √(lcₒc/(cₒ+c))

Explanation: parallel resonant frequency of an oscillator is given by√(lcₒc/(cₒ+c)).

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:

(A) 3 mhz
(B) 0.3 mhz
(C) 6 mhz
(D) 9 mhz

💬 Discuss

✅ Correct Answer: (A) 3 mhz

Explanation: the parallel resonant frequency of a crystal oscillator is given by 1/

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.

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

💬 Discuss

✅ Correct Answer: (A) true

Explanation: in microwave oscillator, for a current to flow in the circuit the negative impedance of the device must be matched with positive impedance. this results in current being non-zero and generates oscillation.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. Any device with negative impedance as its characteristic property can be called:

(A) energy source
(B) energy sink
(C) oscillator
(D) none of the mentioned

💬 Discuss

✅ Correct Answer: (A) energy source

Explanation: a positive resistance implies energy dissipation while a negative resistance implies an energy source. the negative resistance device used in the microwave oscillator, thus acts as a source. the condition xin+ xl=0 controls the frequency of oscillation. xin is the impedance of the negative resistance device.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.

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

💬 Discuss

✅ Correct Answer: (B) false

Explanation: the condition for steady state oscillation in a microwave oscillator is zin=- zl. since this condition is satisfied in the above case, steady state oscillation is achieved.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:

(A) Гin=Гl
(B) Гin=-Гl
(C) Гin=1/Гl
(D) none of the mentioned

💬 Discuss

✅ Correct Answer: (C) Гin=1/Гl

Explanation: the condition for steady state oscillation to be achieved in terms of reflection coefficient is Гin=1/Гl. here Гin is the reflection coefficient towards the reflection coefficient device and Гl is the reflection coefficient towards the load.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.

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

💬 Discuss

✅ Correct Answer: (B) false

Explanation: the condition zin + zl=0 is only a necessary condition for stable oscillation and not sufficient. stability requires that any perturbation in current or frequency is damped out, allowing the oscillator to return to its original state.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.

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

💬 Discuss

✅ Correct Answer: (B) false

Explanation: in a transistor oscillator, a negative resistance one port network is created by terminating a potentially unstable transistor with impedance designed to drive the device in an unstable region.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Q. In transistor oscillators, FET and BJT are used. Instability is achieved by:

(A) giving a negative feedback
(B) giving a positive feedback
(C) using a tank circuit
(D) none of the mentioned

💬 Discuss

✅ Correct Answer: (B) giving a positive feedback

Explanation: oscillators require a device that has high instability. to achieve this condition, transistors are used with a positive feedback to increase instability.

Published by Mr. Dubey ⭐ 111.54K Points at 14-Jun-2020 11:59 am in Antennas and Microwave Engineering

Antennas and Microwave Engineering MCQs | Page - 17

Q. In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:

Q. Parallel resonant frequency of quartz crystal is given by:

Q. The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:

Q. In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.

Q. Any device with negative impedance as its characteristic property can be called:

Q. In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.

Q. For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:

Q. To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.

Q. In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.

Q. In transistor oscillators, FET and BJT are used. Instability is achieved by:

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