# Antennas Questions and Answers – Frequency Independent Antenna – Normal Mode of Radiation

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Frequency Independent Antenna – Normal Mode of Radiation”.

1. In which of the following the radiation of helical antenna is broadside?
a) Normal mode
b) Axial mode
c) Conical mode
d) Beam mode

Explanation: In normal mode of radiation, the radiation is broadside direction. In Axial mode of radiation, it is in end-fire direction. Axial mode is also known as Beam mode.

2. Which of the following is the condition for the normal mode of radiation?
a) The dimensions of antenna must be smaller compared to the wavelength
b) The dimensions of antenna must be approximately equal to the wavelength
c) The dimensions of antenna must be greater compared to the wavelength
d) The dimensions of antenna must be approximately equal to or greater than the wavelength

Explanation: In normal mode, the radiation is normal to the axis of the antenna hence it is broadside directed. The dimensions of the antenna are small compared to the wavelength in normal mode. In axial mode, it is approximately equal to the wavelength. In conical mode, it is greater than wavelength.

3. In which of the following mode of radiation low efficiency and narrow bandwidth is observed?
a) Normal mode
b) Axial mode
c) Conical mode
d) Beam mode

Explanation: The radiation of broadside antenna is normal to the axis line. The radiation of antenna in normal mode is perpendicular to the axis of the antenna and hence it is broadside directed. The drawbacks of the normal mode are its low radiation efficiency and narrow bandwidth.
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4. In normal mode of radiation, far field pattern is independent of number of turns in helical antenna.
a) True
b) False

Explanation: In normal mode, the dimensions of the antenna are small compared to the wavelength. So the current magnitude and phase is constant overall the length. The far field pattern is independent of the number of turns. It considers as a single loop.

5. Which of the following is false regarding normal mode of radiation of helical antenna?
a) The dimensions of the antenna are small compared to the wavelength
b) The far field pattern is independent of the number of turns
c) The current is assumed to vary along the length of the antenna
d) The radiation is normal to the direction of the axis

Explanation: For a helical antenna operating in normal mode, the radiation is normal to the direction of the axis. The antenna dimensions are small compared to the wavelength. So all over the length, the current magnitude and phase is constant. The pattern of far field is independent of the number of turns and it considers as a single loop.
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6. Normal mode of radiation is limited in use because _____
a) it has narrow bandwidth and dependency on small dimensions of the antenna compared to wavelength
b) it has broad bandwidth and independent of antenna dimensions
c) it has narrow bandwidth and is independent of antenna dimensions
d) it has broad bandwidth and dependency on large dimensions of the antenna compared to wavelength

Explanation: The normal mode of radiation depends on the size of the antenna. Its critical dependency on dimensions of antenna which has to be less than the wavelength is difficult and so it causes for narrow bandwidth and low radiation efficiency.

7. In normal mode, the radiation is directed along ______
b) end-fire
c) along the axis
d) in all directions

Explanation: The normal mode of radiation radiates in the direction normal to the axis of the antenna. So radiation is directed in broadside. In Axial mode, it is directed along the end-fire (along the axis of antenna).

8. For a helical antenna radiation, the pitch angleα should be _____
a) 0 < α < 90
b) α=0
c) α=90
d) α=0 or 90

Explanation: The radiation pattern of the helical antenna is a combination of the small dipole and loop antenna. Pitch angle is the tangent of ratio between the spacing and the circumference of the antenna. α=0, then helical antenna becomes loop antenna. α=90, the helical antenna becomes linear antenna.

9. Which of the following is true about normal mode of radiation?
a) The dimensions of the antenna are small compared to the wavelength
b) The radiation is along the axis of the antenna
c) It has high radiation efficiency

Explanation: The normal mode of radiation depends on the size of the antenna. Its critical dependency on dimensions of antenna which has to be less than the wavelength is difficult and so it causes for narrow bandwidth and low radiation efficiency. Radiation is normal to the direction of axis.

10. In normal mode of operation, the radiation is along the end-fire direction.
a) True
b) False

Explanation: In normal mode of radiation, radiation is normal to the direction of axis and is directed in the broadside. The dimensions of the antenna are small compared to the wavelength. In Axial mode, it is end-fire directed.

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