Antennas

Problem:

Consider a linear antenna of length d (d << λ) with a narrow gap in the center for the purposes of excitation.  Assume that the current is sinusoidal and in the same direction in each half of the antenna, having a value of I0 at the gap and falling linearly to zero at the ends.  Find the power radiated in the electric dipole approximation.

Solution:

Problem:

Assume an antenna is aligned with the z-axis and extends from z = -l/4 to z = +l/4.  Assume the current in the antenna varies as I(z,t) = I0sin(ωt)cos(kz).  Calculate the radiation fields ER and BR and the average Poynting vector.

Solution: