# Antennas Questions and Answers – Frequency Independent Antenna – Modes of Radiation

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

1. Which of the following modes of radiation, the radiation of helical antenna is along the end-fire direction?
a) Axial mode
b) Normal mode
c) Perpendicular mode
d) Beam mode and Normal mode

Explanation: In Axial mode of radiation, the radiation is in end-fire direction along the helical axis. In Axial mode of radiation, the dimensions of antenna are approximately equal to the wavelength and spacing space of λ/4. Axial mode is also known as beam mode or end-fire mode. In normal mode, the radiation is perpendicular to axis.

2. In which of the following mode, the radiation is perpendicular to the axis of helical antenna?
a) Normal mode
b) Axial mode
c) Beam mode
d) End-fire mode

Explanation: In normal mode, the radiation is perpendicular to axis. It is also known as perpendicular mode. In this the antenna dimensions are smaller compared to the wavelength. Axial mode is also known as beam mode or end-fire mode. In Axial mode of radiation, the radiation is in end-fire direction along the helical axis.

3. In which of the following mode the dimensions of the antenna must be smaller compared to the wavelength?
a) Normal mode
b) Axial mode
c) Beam mode
d) End-fire mode

Explanation: In normal mode, the radiation is perpendicular to axis. It is also known as perpendicular mode. In this the antenna dimensions are smaller compared to the wavelength.Axial mode is also known as beam mode or end-fire mode. In Axial mode of radiation, the radiation is in end-fire direction along the helical axis.
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4. Drawbacks of the normal mode of radiation in helical antenna are _______
a) low radiation efficiency and narrow bandwidth
b) high radiation efficiency and narrow bandwidth

Explanation: In normal mode, the radiation is perpendicular to axis. The radiation pattern of a helical antenna is a combination of small dipole and loop antenna. In normal mode of radiation, it provides narrow bandwidth and low radiation efficiency.

5. Which of the following is true regarding the axial mode of radiation in helical antenna?
b) Radiation pattern is narrow and no minor lobes are produced
c) Minor lobes are produced only along the direction of helical axis
d) The dimensions of antenna are smaller than the wavelength

Explanation: In Axial mode of radiation, the radiation is in end-fire direction along the helical axis. The radiation pattern of the antenna is broad, directional along axis and produces minor lobes at oblique angles. The dimensions of antenna are approximately in the order of the wavelengths.

6. In which of the following mode, the helical antenna has narrow bandwidth?
a) Normal mode
b) Axial mode
c) Beam mode
d) End-fire mode

Explanation: The radiation pattern of a helical antenna is a combination of small dipole and loop antenna. In normal mode of radiation, it provides narrow bandwidth and low radiation efficiency. Axial mode is also known as beam mode or end-fire mode.

7. In which of the following mode, there are no minor lobes at oblique angles in radiation pattern?
a) Normal mode
b) Axial mode
c) Conical mode
d) Beam mode

Explanation: In normal mode of radiation, it provides narrow bandwidth and low radiation efficiency. In Axial mode of radiation, the radiation is in end-fire direction along the helical axis. The radiation pattern of the antenna is broad, directional along axis and produces minor lobes at oblique angles.

8. In which of the following modes, the dimension of the helical antenna circumference is greater than the wavelength?
a) Normal mode
b) Axial mode
c) Conical mode
d) Beam mode

Explanation: In Axial mode of radiation, the dimensions of antenna are approximately in the order of the wavelengths. In normal mode, dimensions of antenna are smaller compared to wavelength. In conical mode, the circumference of the antenna is greater than the wavelength.

9. The radiation pattern of the helical antenna is a combination of small dipole and loop antenna.
a) True
b) False

Explanation: The helical antenna radiation pattern is a combination of small dipole and loop antenna.If the diameter of the helical antenna is zero (pitch angle 90) then it is linear antenna and when spacing length becomes zero (pitch angle 0) then it acts like a loop antenna.

10. If the spacing between turns of the helical antenna is zero then it acts as a ________
a) Loop antenna
b) Linear dipole
c) Parabolic antenna
d) Log periodic antenna

Explanation: The radiation pattern of a helical antenna is a combination of small dipole and loop antenna. The helical antennas behave like a loop antenna when spacing between turns becomes zero. It becomes a linear dipole when the diameter is zero that means itch angle is zero. Parabolic is a reflector antenna. Helical antenna is a wire antenna.

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