Aperture synthesized radiometer using digital beamforming techniques

Abstract

A digital aperture synthesized radiometer for synthesizing the imaging an image scene. A plurality of antenna arrays receive radiation emitted or reflected from an scene, and an analog to digital coverter converts received radiation into digitized signals. A digital beamformer synthesizes the digitized signals to provide an image corresponding to the scene. The digital beamformer comprises individual digital beamformers which generate a set of fanbeam signals for each array. The beamformers provide for cross track imaging of the scene. A digital interferometer correlates corresponding pairs of fanbeam signals from the two sets of fanbeam signals to produce a chirp signal for each pair. A matched filter processes the chirp signals to transform each chirp signal into a corresponding image point of the scene. This provides for along track imaging of the scene. The beamformers include an amplitude weighting and data turning circuit to reduce fanbeam signal sidelobe levels and eliminate alternate mainlobes from the digitized radiation signals to reduce mainlobe widening. A fast Fourier transform circuit in the beamformers generally comprises a decimation-in-time algorithm implemented by means of a plurality of parallel and cascaded butterfly computation circuits. Image processing methods for achieving digital radiometry are also disclosed.