Scan compensation for array antenna on a curved surface

摘要

A low array antenna having transmit/receive (T/R) modules, which contain a digitally-controlled variable attenuator, for each of the two polarizations (horizontal and vertical). The array has a cylindrically curved surface which closely conforms to the shape of the fuselage of an airborne vehicle or another structure. Each polarization feeds into an elevation beamformer apparatus which provides both a uniform taper and a Bayliss/Taylor taper. As the beam is scanned in elevation, the amplitude taper is adjusted via the variable attenuator to control the taper of a sum pattern and thereby achieve low sidelobe far field sum patterns. The same attenuators that are used for the sum pattern also feed a difference network. The T/R module attenuators are set to yield the desired low sidelobe sum illumination for a desired elevation scan angle. As the array is steered in elevation, the Bayliss difference taper is distorted since the fixed elevation beamformer cannot adjust the difference pattern for the new scan angle. A T/R module is provided at each column of the array to combine the distorted Bayliss difference pattern with the compensated Taylor sum pattern output. This combining permits the distorted Bayliss array illumination to be resymmetrized thereby producing a high quality, low sidelobe, compensated Bayliss far field pattern. This apparatus provides for complete compensation of both sum and difference patterns with only a single attenuator at each element of the array and a simple monopulse feed network.