Adaptive Radar Beacon Forming

Propagation errors along paths between an array radar and a distribution of targets cause degradations in angle measurements and detection range. The overall objective of the research described in this paper was to analyze and demonstrate the use of conjugate reflections for compensating adverse effects of path errors. The effect of reflecting the conjugate of an incident wave is described mathematically and is demonstrated by computer simulation. Repeated conjugate reflections are shown to result in the formation of a single beam usually focussed on a target highlight. Echoes from this spatial reference, or "beacon" are shown to provide the means by which aperture phase errors may be effectively compensated. Results of radar simulations include two-way patterns computed for an example involving a distribution of three-point targets and half-wave-length Gaussian aperture errors. Without compensation a gain loss of 12 dB is computed; with error correction, based on echoes from an adaptively focussed beam, the two-way pattern is within a small fraction of a dB of the ideal pattern. The effect of noise on adaptive beacon forming was considered for a case involving one target. Repeated conjugate reflections improve signal-to-noise ratio as long as the effect of noise is less than the effect of aperture dephasing on the power reflected back to the target. An example is presented in which signal-to-noise ratio at the output of the receiver combining network is increased from 4 to 11.8 dB.