SOLVED Numerical's - Antenna Theory - Page 5.
13) A 1-m-long car radio antenna operates in the AM frequency of 1.5 MHz. How much current is required to transmit 4 W of power? SOLUTION: This is a monopole antenna λ = c / f = (3 x 108) / (1.5 x 106) = 200 m In this case, it’s pretty clear that l << λ 14) An antenna located on the surface of a flat earth transmits an average power of 200 kW. Assuming that all the power is radiated uniformly over the surface of a hemisphere with the antenna at the center, calculate (a) The time-average Poynting vector at 50 km, and (b) The maximum electric field at that location. SOLUTION: a) P rad = ∫ P rad . ∂s = P ave . 2πr 2 (hemisphere) P ave = P rad / 2πr 2 = (200 x 10 3 ) / (2π 50 x 10 6 ) 2 =12.73 µW / m 2 P av...