Question

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

The question was posed to me during an interview for a job.

My enquiry is from Frequency Independent Antenna in chapter Frequency Independent Antenna of Antennas

Answer 1

Correct answer is (c) The current is assumed to vary along the length of the antenna

To explain: 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.