Synthesis of Scan- and Frequency-Invariant Low-Sidelobe Tapers for Planar Array Antennas

The impact of the array factor (AF) on the synthesis of a low-sidelobe taper for planar array antennas with a periodic element grid is investigated. A low-sidelobe taper that is synthesized for those far-field directions of the AF belonging to only visible direction, cosine u-v space, can seriously deteriorate with respect to peak sidelobe level (PSLL) when the main beam is scanned or the operating frequency is raised. In order to get a scan- and frequency-invariant taper, its synthesis must comprise all far-field directions of the AF including those of invisible u-v space. This communication describes the Fourier properties responsible for the degradation of taper sidelobe level performance when the taper synthesis excludes the invisible space region of the AF. Examples are presented for a circular array antenna to illustrate the impact of the invisible region of the AF on sidelobe performance. The presented results refer to phase-only and amplitude-only sidelobe tapers. The requirements to realize for aperiodic planar array antennas' scan and frequency proof patterns with invariant PSLL are shortly addressed.