# Microwave Engineering Questions and Answers – Properties of Dividers and Couplers

This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Properties of Dividers and Couplers”.

1. Power dividers and couplers are ______ microwave components used for power division or power combining.
a) Passive
b) Active
c) Linear
d) Non linear

Explanation: When a given input power is to be divided equally at microwave frequencies, power dividers are used. Since couplers and dividers do not store any energy they are called passive microwave components.

2. T- junction is an example for:
a) 2 port network
b) 3 port network
c) 4 port network
d) None of the mentioned

Explanation: A T junction is a 3 port network where the junction is excited at one of the port, output is measured at another port, with the third port terminated with a known impedance.

3. A T junction has a 3×3 ‘s’ matrix.
a) True
b) False

Explanation: ‘n’ port microwave network is represented as n×n s matrix. Characteristics of a microwave network can be known by analyzing his s matrix. A T junction has 3 ports. Hence, they are represented as a 3×3 matrix.

4. If a device is passive and contains no anisotropic elements, then the device is_______ network.
a) Reciprocal
b) Non reciprocal
c) Lossless
d) Lossy

Explanation: If a device is passive, it does not store any energy and does not contain any sources. It then acts as a reciprocal network. That is, when the input and output ports are interchanged, the power delivered remains the same.

5. Scattering matrix of a reciprocal network is:
a) Symmetric
b) Asymmetric
c) Identity matrix
d) Null matrix

Explanation: For a reciprocal network, when the output and input ports are interchanged/ the power delivered remains the same. Hence in the S matrix Sij=Sji. This condition is satisfied by a matrix that is symmetric.

6. If all the ports of a microwave network are matched, then the diagonal elements of the S matrix of the network is zero.
a) True
b) False

Explanation: When all the ports of a microwave network are matched, no power is reflected back to the port that is excited by the source. Since no power is reflected back, the elements Sii of the S matrix become zero.

7. If a microwave network is lossless, then S matrix of the microwave network is:
a) Unitary
b) Symmetric
c) Identity matrix
d) Zero matrix

Explanation: If a microwave network is lossless, law of energy conservation requires that the condition for example, │S12│2+│S13│2= 1. This condition has to be satisfied for a 3 port network. This can be generalized for any n port network.

8. A lossless reciprocal 3 port network can be matched at all the three ports.
a) True
b) False

Explanation: A lossless three port network can be only matched at 2 ports. It not possible for the S matrix of a 3 port network to satisfy all the above conditions .This would violate the law of conservation of energy.

9. A circulator is a 3 port network that allows energy flow in clockwise direction only.
a) True
b) False

Explanation: A circulator is a 3 port device that allows energy flow in only one direction. The direction of flow is either clockwise or counter clockwise. Bothe the directions are not simultaneously allowed in a circulator.

10. The diagonal elements of the S matrix of an improperly matched circulator is zero.
a) True
b) False

Explanation: If the three ports of a circulator are not properly matched, it would result in the backward flow of power to the previous ports. Hence, the diagonal elements will not be zero due to improper matching as they signify the reflection of energy back to the same port.

11. Coupling factor of a directional coupler must be maximum and is a key factor that determines the performance of the coupler.
a) True
b) False

Explanation: Coupling factor indicates the fraction of input power that is coupled to the output port. If a directional coupler has higher coupling factor, maximum power is obtained at the output port with low loss.

12. Directivity of a directional coupler signifies the direction of power flow in the coupler.
a) True
b) False

Explanation: Directivity is the measure of the directional coupler’s ability to isolate forward and backward waves. Directivity is also defined as the ratio of power at the output port to the power at the isolated port.

13. Isolation of a directional coupler is a measure of the:
a) Power delivered to the uncoupled port
b) Power delivered to the coupled port
c) Power delivered to the second port
d) None of the mentioned

Explanation: In a directional coupler, there exists a port called the isolated port through which no power is received and is isolated from the remaining ports of the coupler. Isolation of a directional coupler is a measure of the power delivered to the uncoupled port.

14. Insertion loss is the power delivered to the through port.
a) True
b) False

Explanation: In a directional coupler, the second port is called is called the through port and the third port is called the output port. When power flows from port 1 to output port, the power measured at port 2 can be termed as insertion loss.

15. In a symmetric coupler, the power delivered to the through port and output port are equal.
a) True
b) False

Explanation: A symmetric coupler is the one which delivers equal amount of power to both port 2 and port 3 of the directional coupler. The signals t these ports are out of phase by 900.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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