Question

The radiation resistance of a monopole of height 1cm and operating at frequency 100MHz is ____ Ω.

(a) 4.83m

(b) 4.38k

(c) 4.38m

(d) 4.83k

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

This interesting question is from Radiation in section Radiation, Baluns & Polarization of Antennas

Answer 1

The correct choice is (c) 4.38m

The explanation is: The radiation resistance of a monopole is 1/8 times the current element.

\(R_{rad}=10\pi^2 (l/\lambda)^2\)

For a monopole height h= l/2 => l= 2h

\(R_{rad}=10\pi^2(\frac{2h}{\lambda})^2=40\pi^2 (\frac{hf}{c})^2=40\pi^2 (\frac{1×100×10^6}{3×10^{10} })^2=4.38m\Omega\)