Which of the following is the most necessary for an electric field to exist?

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.

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.

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.