Microwave Engineering Multiple Choice Questions on “Excitation of Resonators”.
1. The level of coupling required between a resonator and its attached circuitry is a standard and independent of the application where coupling is required.
A. true
B. false
Answer: B
Clarification: The level of coupling required between a resonator and its attached circuitry depends on the application. A waveguide cavity to a frequency meter is loosely coupled to maintain high Q and good accuracy.
2. A measure of the level of coupling between a resonator and a feed is given by:
A. coupling coefficient
B. power transfer coefficient
C. voltage coefficient
D. reflection coefficient
Answer: A
Clarification: Coupling coefficient tells how the resonator is coupled to the external circuitry. A resonator can be coupled in three ways. They can be under coupled, critically coupled or over coupled.
3. To obtain maximum power transfer between a resonator and feed line, the resonator should be matched to the load at:
A. resonant frequency
B. cutoff frequency
C. zero frequency
D. none of the mentioned
Answer: A
Clarification: In order to obtain a maximum power transfer between a resonator and a feed line, the resonator should be matched to the feed line at the resonant frequency of the resonator which is coupled.
4. When impedance matching is done between a resonator and a feed line, the condition for impedance matching is:
A. R=Z0
B. R=Z0/2
C. R=2Z0
D. R=√Z0
Answer: A
Clarification: If R is the resistance of the series RLC circuit and Z0 is the characteristic impedance of the feed line, for proper coupling their impedance has to be matched. This is the condition for impedance matching between a feed line and a resonator.
5. Coupling coefficient Q can be defined as the ratio of unloaded Q to external Q.
A. true
B. false
Answer: A
Clarification: Coupling coefficient Q defined as the ratio of unloaded Q to external Q can be applied to both series resonance and parallel resonance circuits. For series resonant circuits, coupling coefficient is defined as the ratio of characteristic impedance of feed line to the resistance in the resonant circuit.
6. When the coupling coefficient is lesser than one, the resonator is over coupled to the feed line.
A. true
B. false
Answer: B
Clarification: When the coupling coefficient is less than one, the resonator is under coupled to the feed line. For a series resonant circuit, resonator is under coupled implies that the resistance in the resonator is greater than the characteristic impedance of the transmission line.
7. Direct measurement of the unloaded Q of a resonator is not possible.
A. true
B. false
Answer: A
Clarification: Direct measurement of the unloaded Q of a resonator is not possible because of the loading effect of the measurement system, but it is possible to determine unloaded Q from measurements of the frequency response of the loaded resonator when it is connected to a transmission line.
8. For practical applications cavity resonators can be modified as per the requirement of the application where it is used.
A. true
B. false
Answer: A
Clarification: Small changes in the cavity resonator can be made by changing their shape, or by introducing small pieces of dielectric or metallic materials. The resonant frequency of a cavity resonator can be easily tuned with a small screw that enters the cavity volume or by changing the size of the cavity by a movable wall.
9. When coupling coefficient is 1, the resonator is ________ to the feed line.
A. under coupled
B. over coupled
C. critically coupled
D. none of the mentioned
Answer: C
Clarification: The resonator is critically coupled to the feed line when the coupling coefficient is 1. Maximum power is transferred between the resonator and the feed line since the resistance of the resonator is equal to the characteristic impedance of the transmission line.
10. In aperture coupling, a small aperture in the transverse wall of the waveguide acts as:
A. shunt inductance
B. shunt capacitance
C. series inductance
D. series capacitance
Answer: A
Clarification: In aperture coupling, a small aperture is made in the transverse wall of the cavity which is to be coupled to an external microwave circuit. This aperture made in the transverse wall of the cavity acts as a shunt inductance.
,