Passive Distributed Aperture Radar Imaging Method Based on Unknown Waveform Modeling

Passive radar uses external illuminators to detect and track instead of radiating electromagnetic waves itself, so it has good electronic countermeasures characteristics, and can save system cost and frequency band resources. In passive distributed aperture configuration, the distribution of each transmitting unit and receiving unit is arbitrary, meantime the spacing of array elements can be 100 or 1000 times of wavelength, which is suitable for the flexible configuration of radar. Based on the consideration of the residual direct wave, this paper studies a passive distributed aperture radar imaging method using the correlation of transmitted waveforms. By modelling the unknown signal transmitted by the illuminators of opportunity (IO) as an autoregressive process (AR), the time correlation is estimated and applied to passive imaging. Then, the correlation of emission waveform and unknown parameters in imaging model are estimated jointly by expectation maximization (EM) algorithm. Finally, passive imaging is realized on the basis of generalized likelihood ratio test (GLRT). The effectiveness of this method is verified by simulation experiments.