Ambiguity suppression in a multiple beam radar

Phased array radars facilitate beam-scanning versatility that was not possible with traditional mechanically scanned radars; specifically, that the advent of electronic beam steering has allowed antennae to scan a wider angular volume per unit time than was previously achievable. This paper develops an idea proposed by DERA Malvern in which this beamforming versatility is exploited by insertion of further pulse trains in the otherwise redundant pulse repetition interval (PRI). Associating these pulse trains with spatially diverse transmit beams formed by such a phased array results in a stare-while-scan (SWS) radar, in which the multiplicity of beams allow the radar to observe a number of directions simultaneously. Such a system would bring the twin advantages of considerable gain with integration of pulses and the provision for realisation of new detection strategies. SWS systems, however, suffer from severe ambiguities caused by imperfect spatial separation between beams, rendering a multiple beam system ambiguous even if its constituent beams contain range unambiguous pulses. Fortunately, these ambiguities can be mitigated by employing a combination of spatial, waveform, frequency and time diversity. The techniques for ambiguity suppression in a multiple beam radar system are the focus of this paper, and are discussed with reference to a conceptual system. The WEFTDAR (Waveform Enhanced in Frequency and Time with Direction of Arrival), as it was termed, achieved beam-to-beam ambiguity suppression of 35 dB by the use of a combination of these diversity techniques. Further increases in this figure are thought to be possible with the use of the AD-MUSIC direction of arrival (DOA) technique.