# Electromagnetic Theory Questions and Answers – Types of Waveguides

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This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Types of Waveguides”.

1. The phenomenon employed in the waveguide operation is
a) Reflection
b) Refraction
c) Total internal reflection

Explanation: The waveguides use total internal reflection phenomenon to transmit the waves passing through it. Thus the acceptance angle and critical angle are important for effective transmission.

2. The dominant mode in waveguide is the mode which has
a) Highest frequency
b) Highest wavelength
c) Lowest phase constant
d) Highest attenuation

Explanation: The dominant mode is the mode which has the minimum frequency or maximum wavelength available for propagation of the waves.

3. The modes are calculated from which parameter?
a) Frequency
b) Wavelength
c) Phase constant
d) V number

Explanation: The modes are calculated from the V number of the waveguides. It is given by M= V2/2.

4. The circular waveguides use which function in the frequency calculation?
a) Laplace function
b) Schottky function
c) Bessel function
d) Transfer function

Explanation: The circular or cylindrical waveguides use the Bessel function for the frequency calculation of a particular mode.

5. The scattering parameters are used to indicate the
a) Permittivity and permeability
b) Electric and magnetic field intensities
c) Reflection and transmission coefficients
d) Frequency and wavelength

Explanation: The scattering matrix consists of the transmission coefficients in the main diagonal and the reflection coefficients in the opposite diagonal.

6. Which of the following two parameter models cannot be used to represent a transmission line?
a) H parameter model
b) T parameter model
c) ABCD parameter model
d) S parameter model

Explanation: The T, ABCD and S parameter models are used in the transmission line modelling. The h parameter is not used for the same.

7. For the matched line, the parameters S12 and S21 are
a) 1
b) 0
c) -1
d) ∞

Explanation: The parameters S12 and S21 are the reflection coefficients. For a matched line, the reflection coefficients are zero. Thus the parameters S12 and S21 are also zero.

8. The waveguides are materials with characteristics of
a) Low bulk resistivity
b) High bulk resistivity
c) High conductivity
d) Low conductivity

Explanation: Generally, the waveguides are made of materials with low bulk resistivity like brass, copper, silver etc. But if the interior walls are properly plated, it is possible with poor conductivity materials too. It is even possible to make plastic waveguides.

9. The parameters S11 and S22 indicate the transmission coefficients. State true/false.
a) True
b) False

Explanation: In a scattering matrix, the parameters S11 and S22 indicate the transmission coefficients and the parameters S21 and S12 indicate the reflection coefficients.

10. The waveguides increase the transmission of the electromagnetic waves. State true/false.
a) True
b) False

Explanation: The waveguides aid in effective transmission of the electromagnetic power from the source antenna to the destination antenna.

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