Method and apparatus for processing synthetic aperture aerial signals

Abstract

A method and apparatus of deriving a directional polar diagram from the signals R received by a synthetic-aperture aerial (in direction-finding applications), or P from such an aerial (in radio-beacon applications), these signals including a carrier of frequency .omega. which is phase-modulated at the scanning frequency .omega..sub.m of the individual aerials. The method comprises generating an "estimated" signal (26) of frequency .omega. phase-modulated at frequency .omega..sub.m, and multiplying (25) the generated signal by the received signal to derive an output which includes a selectable Bessel Function (J.sub.O) representing the directional polar diagram. The phase (with circular aerial arrays) (27) or amplitude (with linear aerial arrays) of .omega..sub.m as applied to phase-modulate the generated signal is controlled to maximize or minimize, as appropriate, the selected Bessel Function and thereby control the bearing direction of the polar diagram. The zero-order Function J.sub.O gives a lobe maximum in the bearing direction, the higher orders, J.sub.1, J.sub.2, etc. a lobe null. The phase difference between .omega. in the generated and received signals is averaged-out by shifting the frequency of the former by a increment .omega..sub.x.

Dependencies are inferred from the claim text.