A technique to increase the scanning rate of a phased array

Severe weather phenomena develop so fast that update time for radar remote sensing should be less than 1 min. The update time can be reduced with an agile-beam radar that steers its beam electronically. To reduce the update time on a prototype of a S band phased array radar (PAR) located in Norman, OK, multiplexing of radar beams, oversampling and whitening in range, and adaptive scanning have been tested. The update time can be also reduced with an imaging radar that transmits a wide beam and forms multiple receiving beams of a phased array. The major pitfall of this approach for weather applications is a reduced radiation power density of the transmit beam and consequently reduced detection capability.

The update time of a PAR can be reduced by switching the beam directions of each of several pulses transmitted in rapid succession so that multiple beams in transmit can be formed. Return signals from these beams can then be received simultaneously. To isolate weather signals, phase coding for every transmit pulse could be employed. This technique is a particular implementation of the MIMO radars (Multiple In Multiple Out).

In this communication, we analyze an approach to isolate returns from different directions using the multiple transmit beams technique. This approach is based on features of antenna patterns and does not use pulse coding and frequency agile methods. The new technique is described using the theoretical and measured antenna patterns of the WSR-88D which is the benchmark for a weather PAR. The technique is applied to data collected with a WSR-88D using the measured antenna radiation pattern. It is shown that the technique allows separations of returned voltages from different transmitted beams with relative signal powers of 100 dB. This isolation is sufficient for weather applications.