Microwave Engineering Multiple Choice Questions on “Ferrite Isolators”.
1. Ferrite isolators are ____ port microwave devices.
A. Two
B. Three
C. Four
D. None of the mentioned
Answer: A
Clarification: Ferrite isolators are two port devices having unidirectional transmission characteristics. Isolator provides isolation between the two ports and the power flow occurs only in one direction.
2. The matrix of an ideal isolator is not ______
A. Unitary
B. Symmetric
C. Lossless
D. None of the mentioned
Answer: A
Clarification: Ferrite isolator allows wave propagation in only one direction and attenuates propagation in the other direction. So the isolator is lossy. Since the isolator is lossy, the scattering matrix of isolator is not unity.
3. A very common application of isolator is to provide isolation between a low power source and the load.
A. True
B. False
Answer: B
Clarification: Isolators have a wide variety of applications. The most common among them is the use of an isolator between a high-power source and a load to prevent the possible reflections from damaging the source. An isolator can be used in place of a matching network, but it should be realized that any power reflected from the source is absorbed by the isolator.
4. The attenuation of a ________ is very large near the gyro magnetic resonance of the ferrite.
A. Linearly polarized wave
B. Circularly polarized wave
C. Left polarized wave
D. Right polarized wave
Answer: B
Clarification: The attenuation of the circularly polarized wave is very large near the gyro magnetic resonance of the ferrite, while the attenuation of the wave propagating in the opposite direction is very small.
5. The isolators constructed using ferrite materials must operate at:
A. Gyro magnetic resonance
B. Magnetic resonance
C. Isolator resonance
D. None of the mentioned
Answer: A
Clarification: The attenuation of the circularly polarized wave is very large near the gyro magnetic resonance of the ferrite, while the attenuation of the wave propagating in the opposite direction is very small. Isolator constructed using ferrite must hence operate at gyro magnetic resonance.
6. Forward attenuation provided by a resonance ferrite isolator is:
A. Zero
B. Low
C. High
D. None of the mentioned
Answer: B
Clarification: Zero forward attenuation cannot be obtained in resonance isolators because the internal magnetic field is not truly circularly polarized. Because of this, there is some amount of forward attenuation in the isolator.
7. An isolator has a very large operating bandwidth and independent of any isolator parameter.
A. True
B. False
Answer: B
Clarification: The bandwidth of an isolator is relatively narrow, dictated essentially by the line width ∆H of the ferrite material.
8. The length of a ferrite slab required operating with a minimum forward insertion loss and 30 dB reverse attenuation and the reverse attenuation at this point is:
A. 3 cm
B. 2.4 cm
C. 4 cm
D. 3.6 cm
Answer: B
Clarification: Length of the ferrite slab required is equal to the ratio of the minimum forward insertion loss to the reverse attenuation at the point. Substituting the given values in the above equation, length of the ferrite slab is 2.4 cm.
9. The electric field distribution of the forward and reverse waves in a ferrite slab-loaded waveguide is quite different. This property is used in:
A. Field displacement resonator
B. Resonance isolator
C. Waveguide isolator
D. None of the mentioned
Answer: A
Clarification: In a field displacement isolator, electric field distribution of the forward and reverse waves in a ferrite slab-loaded waveguide is different. The electric field for the forward wave can be made to vanish at the side of the ferrite slab.
10. Field displacement isolators require higher bias field than resonance isolators.
A. True
B. False
Answer: B
Clarification: Field displacement isolators have much smaller bias field requirement since it operates well below gyro magnetic resonance. This property of field displacement isolator make it more preferred than resonance isolators.