# Microwave Engineering Questions and Answers – Wilkinson Directional Couplers

This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Wilkinson Directional Couplers”.

1. Theoretically, the output power at the isolated port of a directional coupler is zero.
a) True
b) False

Explanation: The waves meeting at the isolated port of a directional coupler from 2 different paths traversed by them are out of phase and cancel each other. Hence theoretically, output at isolated port is 0.

2. Bethe hole coupler has a small hole that is used to couple power from one port to another.
a) True
b) False

Explanation: Bethe Hole coupler is formed by coupling one waveguide to another through a small hole in the common broad wall between the two waveguides.

3. The coupling in a Bethe Hole coupler depends on the position of the hole.
a) True
b) False

Explanation: While designing a Bethe Hole coupler, the position of the hole in the broader dimension of the waveguide plays a major role in the amount of signal coupled from one waveguide to another.

4. As the radius of the coupling hole in the Bethe hole coupler increases, signal coupled.
a) Increases
b) Decreases
c) Remains a constant
d) None of the mentioned

Explanation: As the radius of the coupling Hole increases, the amount of power coupled from one waveguide to another. This parameter is taken care of while designing a Bethe hole coupler for a specific design.

5. A major disadvantage of single hole coupler is:
a) Low output power
b) Lower operating bandwidth
c) Complex construction
d) Bulk size

Explanation: The major disadvantage of single hole couplers is that it has lower bandwidth in terms directivity. This problem is overcome by designing multi hole couplers to enhance the bandwidth.
Sanfoundry Certification Contest of the Month is Live. 100+ Subjects. Participate Now!

6. In a 2 hole waveguide coupler the spacing between the 2 holes made in the broader dimension of the waveguides is λg/2.
a) True
b) False

Explanation: The spacing between the holes of a 2 hole directional coupler is λg/4 where λg is the guide wavelength. A phase difference of 900 is present between the signals at the 2 holes of the coupler.

7. For a 4 Hole directional coupler, the plot of frequency v/s directivity has:
a) 4 peaks
b) 2 peaks
c) 3 peaks
d) 8 peaks

Explanation: Since 4 holes are made between the waveguides in order to couple power, due to the addition of the in phase components at these holes, 4 peaks are observed in the plot.

8. The plot of frequency v/s coupling co-efficient is a straight line parallel to X axis.
a) True
b) False

Explanation: Coupling coefficient signifies the amount of input power coupled to the output. When the input and output ports are matched, the gain is a constant value along a wide range of frequencies.

9. The directivity of a Bethe hole coupler is defined as the ratio of:
a) Backward wave to the forward wave
b) Forward wave to the backward wave
c) Impedances of the 2 waveguides
d) None of the mentioned

Explanation: Directivity of a Bethe hole coupler is the ratio of a backward wave to the forward wave at the hole made for coupling between the 2 waveguides.

10. The characteristic impedance of a Bethe hole coupler for operation at 9 GHz frequency is :
a) 550.9 Ω
b) 259 Ω
c) 284.6 Ω
d) None of the mentioned

Explanation: For X band waveguide at 9 GHz, constants of the waveguide dimension and other parameters are predefined as standards. For the given condition, the characteristic impedance of the waveguide used is 550.9 Ω.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
To practice all areas of Microwave Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]