Question

Which of the following is true?

(a) Radiative Field < 0.62\(\sqrt{\frac{D^3}{λ}}\)

(b) Reactive Field < 0.62\(\sqrt{\frac{D^3}{λ}}\)

(c) Fresnel Field << 0.62\(\sqrt{\frac{D^2}{λ}}\)

(d) Near field > \(\frac{2D^2}{λ}\)

The question was asked in an interview for internship.

This intriguing question originated from Near Field and Far Field in division Modern Antennas & Antenna Measurements of Antennas

Answer 1

Right answer is (b) Reactive Field < 0.62\(\sqrt{\frac{D^3}{λ}}\)

To elaborate: The characteristics of EM fields vary with distance from the antenna. It is divided into two regions. The region next to the antenna is the near field region and the region Far field region > \(\frac{2D^2}{λ}\). Reactive field < 0.62\(\sqrt{\frac{D^3}{λ}} < \,Radiative\, field\, < \frac{2D^2}{λ}\).