Mutual coupling compensation for small, circularly symmetric planar antenna arrays

A method is developed for compensating for the effects of mutual coupling in small, circularly symmetric planar antenna arrays, such as those used as feeds for parabolic reflector antennas. The array excitation is first broken down into a series of orthogonal circularly symmetric phase modes, and the compensation may then be achieved by means of fixed compensating impedance matches at the phase-mode excitation ports. After application, the compensation is independent of the subsequent aperture excitation. In addition, the method is applied to four-element planar arrays used as a monopulse cluster feed for a parabolic reflector. Although this method was developed to physically compensate for mutual coupling, the concept may also be used to compute the correct array excitation needed to achieve this compensation.