Which of the following is not true?

A transmission line must not radiate energy

A conductor carrying alternating current radiates

Antennas are transmission lines which are made to radiate energy

A parallel wire transmission, when left open, does not radiate

Correct Answer : A parallel wire transmission, when left open, does not radiate

Explanation : If a parallel-wire transmission line is left open, the electric and magnetic fields escape from the end of the line and radiate into space. This radiation, however, is inefficient and unsuitable for reliable transmission or reception.

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Why is the boom of the yagi antenna connected to a metal mast and electrical ground?

Lightning protection

Increased bandwidth

Better signal directivity

To avoid short circuiting

Correct Answer : Option (A) : Lightning protection

Explanation : The centers of the parasitic elements are neutral electrically; these elements can be connected directly to the boom. For the best lightning protection, the boom can then be connected to a metal mast and electrical ground.

Which of the following is not one of the types of driven array antenna?

End fire antenna

Rectilinear antenna

Broadside antenna

log periodic antenna

Correct Answer : Option (B) : Rectilinear antenna

Explanation : Each element in a driven array antenna receives RF energy from the transmission line, and different arrangements of the elements produce different degrees of directivity and gain. The three basic types of driven arrays are the collinear, the broadside, and the end-i re. A fourth type is the wide-bandwidth log-periodic antenna.

What is the length of the shortest element in the yagi antenna?

One quarter the wavelength of the lowest frequency

One half the wavelength of the lowest frequency

One quarter the wavelength of the highest frequency

One half the wavelength of the highest frequency

Correct Answer : Option (D) : One half the wavelength of the highest frequency

Explanation : The lengths of the driven elements vary from long to short and are related logarithmically. The longest element has a length of one-half wavelength at the lowest frequency to be covered, and the shortest element is one-half wavelength at the higher frequency. The spacing is also variable.