Switched parasitic feeds for parabolic antenna angle diversity

Abstract

The radiation direction from a parabolic dish antenna can be electronically controlled through the use of a switched parasitic element closely coupled to a dipole feed. Through the application of a dc voltage, the half‐wavelength‐long parasitic element is switched between open and short circuit using a p‐i‐n diode at its center. With a parasitic element vertically offset from the horizontal dipole, the performance of the antenna in both switch positions has been optimized. At 1.5 GHz, using a 2.4 m diameter reflector, beam skewing on the order of 1.5° at the −6 dB point can be achieved for a feed element spacing of 0.6 wavelengths. At a parasitic element spacing of 0.5 wavelengths, the main lobe is better than 15 dB above the unshifted null. The analysis of such a structure requires the calculation of the current in both the driven element and the parasitic element and the summation of their fields on the surface of the reflector independently.