Question

What is the radiation resistance of a short dipole of length L?

(a) 20π^2 \((\frac{L}{\lambda})^2\)

(b) 80π^2 \((\frac{l}{\lambda})^2\)

(c) 40π^2 \((\frac{l}{\lambda})^2\)

(d) 160π^2 \((\frac{l}{\lambda})^2\)

This question was posed to me in exam.

My doubt is from Radiation Resistance topic in section Antenna Parameters of Antennas

Answer 1

Correct option is (a) 20π^2 \((\frac{L}{\lambda})^2\)

For explanation I would say: Radiation resistance of a Hertzian dipole of length l is given by R=80π^2 \((\frac{l}{\lambda})^2\)

Then short dipole is of length l/2, so the radiation resistance is given by R=80π^2\((\frac{L/2}{\lambda})^2=20\pi^2 (\frac{L}{\lambda})^2.\)