The TechSat21 space-based radar employs a cluster of free-floating satellites, each of which transmits its own orthogonal signal and receives all reflected signals. The satellites operate coherently at X-band. The cluster forms essentially a multi-element interferometer with a concomitant large number of grating lobes and significant ground clutter. A novel technique for pattern synthesis in angle-frequency space is proposed, which exploits the double periodicities of the grating lobes in the angular domain and of the radar pulses in the frequency domain, and allows substantial gains in clutter suppression. Gains from 7 to 17 dB relative to the normal random, sparse array appear feasible.

: The purpose of this report is to show that deep nulls can be imposed at specified locations in planar array antenna using phase-only control of coarsely quantized phase shifters. This is done by using the number of phase shifters available for control in the columns of the array to compensate for the small number of bits of the individual phase shifters. Null synthesis algorithms are derived to calculate phase shifts to impose nulls in the phi equals 0 degrees pattern cut of planar array antenna patterns. Results of calculations are presented in this report. Keywords include: Planar array antennas, Phase quantization, Phase-only weight control, and Null synthesis.

The synthesis, analysis, and experimental measurements of a metal grid angular filter are described. Angular filters are devices that can be added to existing antennas in order to reduce the radiation over a specified angular region while allowing radiation over other angular sectors to pass relatively unaffected. The behavior of this angular filter, both in frequency and angle, is analyzed in this paper, and these results are compared with measurements.