NCEES ELECTRONICS PROBLEM 127

Problem 127 asked the form of the current of the antenna. Anyone knows how to solve it?

The radiation pattern of a wire of length L (centered at x=0,y=0 and z=0) is shown in the figure. The pattern is normalized such that the magnitude of radiation is one in the directions of maximum radiation. The wire i slocated along the y axis of the radiation pattern as shown by the broader line. The wire has a time varying current distributin along its length. The current distribution that would give the pattern shown is most nearly: the answer is A. I*cos(pi*y/l).

Does anyone know how to solve it?