# Microwave Engineering Questions and Answers – Ferrite Circulators

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This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Ferrite Circulators”.

1. ________ is a three-port microwave device that can be lossless and matched at all spots.
a) Hybrid junction
b) Magic Tee
c) Circulator
d) Isolator

Explanation: A circulator is a three-port microwave device that can be lossless and matched at all ports; by using the unitary properties of scattering matrix it is proved that such a device must be non-reciprocal.

2. The total number of ones in the scattering matrix of an ideal circulator is:
a) 4
b) 3
c) 2
d) 5

Explanation: Since the circulator is matched at all the ports, the diagonal elements are zero. As the circulator allows power flow in only one direction, only one of the elements in each row has a 1 in the matrix. With three rows, there are three ones.

3. There is no method in which the scattering matrix of the opposite circularity can be obtained from the matrix we have.
a) True
b) False

Explanation: By transposing the port indices of the existing matrix, the opposite circulatory can be obtained. For example, if S13 is a 1 in the given circulator, then S31 is automatically one in the opposite circulator.

4. Practically, opposite circulatory in a ferrite circulator can be obtained by:
a) Changing the order of port operation
b) Impedance matching the input ports
c) Changing the polarity of the magnetic bias field
d) None of the mentioned

Explanation: For a ferrite circulator, opposite circulatory can be produced by changing the polarity of the magnetic bias field. This change in polarity causes power to flow in opposite direction but only in one direction.

5. A circulator device can also used as an isolator with a few modifications.
a) True
b) False

Explanation: A circulator can be used as an isolator by terminating one of the circulator ports with known impedance so that the remaining two ports are used for operation. As power flow occurs only in one direction in these two ports, they can be used as isolators.

6. In the scattering matrix representation of a non-ideal circulator, the diagonal elements of the matrix are:
a) Zero
b) One
c) Reflection coefficient Г
d) None of the mentioned

Explanation: In a non-ideal circulator, the three ports of the circulator are not properly matched and hence there will be some reflection back to the same ports. This impedance mismatch can be represented by the reflection co-efficient Г.

7. In a stripline junction circulator, the ferrite material is present in the form of a:
a) Slab
b) Ferrite disk
c) Ferrite material is not used in a microstrip circulator
d) Ferrite cubes

Explanation: In a stripline junction circulator, two ferrite disks fill the space between the center metallic disk and the ground planes of the stripline. Three striplines are attached to the periphery of the center disk and the ground plane on the stripline.

8. The dielectric resonator in the circulator has a single highest order resonant mode.
a) True
b) False

Explanation: In operation of a microstrip circulator, the ferrite disks form a dielectric resonator; in the absence of the bias field this resonator has a single lowest order resonant mode with a cos φ dependence.

9. In the plot of the magnitude of electric field around the periphery of the junction circulator, the curve has:
a) Three peaks
b) Two peaks
c) Four peaks
d) None of the mentioned

Explanation: In the plot of the magnitude of electric field around the periphery of the junction circulator, the curve has three peaks. These three peaks are due to the three ports of the circulator where the field measured is maximum.

10. In the non-ideal scattering matrix representation of the circulator, the attenuation constant and phase constant α, β respectively are approximated as 1.
a) True
b) False

Explanation: In the non-ideal scattering matrix representation of the circulator, the attenuation constant and phase constant α, β respectively are approximated in terms of the reflection coefficient which represents the impedance mismatch in the network. Α is approximated as 1-Г2 and β is approximated as Г.

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