Question

If the power radiated by a half wave dipole is 100mW then power radiated by a quarter wave monopole under same current input is _____

(a) 50mW

(b) 200mW

(c) 100mW

(d) 50W

I had been asked this question at a job interview.

My question is from Power Radiation from Half Wave Dipole topic in section Antenna Parameters – II of Antennas

Answer 1

Correct answer is (a) 50mW

To elaborate: Average Power radiated from the half-wave dipole \(P_{avg-hlf}=I_{rms}^2 R_{hlf}\)

⇨ \(\frac{P_{avg-hlf}}{P_{avg\, mono}} = \frac{R_{hlf}}{R_{mono}} = \frac{73}{36.5}=2\) (under same current)

\(P_{avg \,mono}=\frac{P_{avg-hlf}}{2}=\frac{100mW}{2}=50mW.\)