Array Geometry Effects on Digital Beamforming for Multi-Channel Passive Radar Systems

Passive radar which uses the so called "signal of opportunities" has become very popular in last decade or so. These radars provided the advantages of ease of use, and covertness, which arises because of the use of third-party free signals. Since there is no control on the transmitted waveform, therefore the signal processing involve in passive radar is more complicated and challenging. In passive radar, the typical cross-ambiguity function (CAF) is used to form the final Doppler-range plot which can be used for detection. The cross-ambiguity function uses the signal scattered from target and pure reference signal coming from main transmitter. Initially the passive radar system utilizes two antenna setup to collect these two signals. One antenna is used to collect the so called reference signal and the other is used to collect the target echo corrupted by very strong reference signal. Therefore, the first step is to clean this target signal by using classical interference cancelation algorithm based on various types of adaptive filters. Later on, multi-channel passive radar systems were developed for providing additional gain in suppressing reference signal by using digital beamforming (DBF). The use of digital beamforming in combination with interference cancelation provides enough gain to acquire a clean target signal, thus improving the final detection by CAF. These multi-channel system include an array of antennas, typical configured as either uniform linear array (ULA) or uniform circular array (UCA). The aim of this paper is to cover various array configuration and there effect on suppressing the reference signal by using DBF. Various array configuration will be presented along with digital beamforming algorithms being implemented by optimizing the array factor. The array configuration which will be covered include linear, circular and rectangular. The optimization based DBF will be presented with the constraint of very low level of side lobes. The effect of various array configuration on the efficient cancelation of reference signal will be presented using simulated data.