Two half – wave dipole antennas placed as shown in the figure are exited with sinusoidal varying currents of frequency 3 MHz and phase shift of π/2 between them (the element at the origin leads in phase). If the maximum radiated E – field at the point P in the x – y plane occurs at an azimuthal angle of 60°, the distance d (in meters) between the antennas is ______
