assive radars are considered as low-priced, undetectable and electronic warfare resistant radars due to their lack of transmitter. The idea of using available signals in the environment (e.g. FM radio, analog TV, GSM, etc.) as the radar transmitter has been considered since the early years of the radar invention. Detection and tracking of the targets in passive radars require advanced methods of signal processing, and this in turn significantly increases the computational cost of the system. Considering the fact that in passive radar the receiver has no information about the waveform sent by the transmitter, a reference channel is generally required to collect the transmitter signals as well target channels to collect the target signals. After the development of the digital processors in the recent years, extensive research has been conducted in this field and passive radars have been utilized in many applications. The main interference in passive radars is the direct path and multipath signals or clutters. The presence of these signals in the receiver’s target channel will degrade the detection performance and severely limit the detection range. Therefore, the cancellation of these signals before the matched filter processing is necessary. So in this thesis, after introducing the passive radars, this problem has been investigated and the methods (which are mostly adaptive filter methods) have been discussed. Considering the characteristics of FM signal, a method has been proposed based on subband adaptive filter, and the cancellation methods have been compared in terms of target detection and computational complexity. Another important issue in any radar is target detection, which is in fact their main function. Many studies have been done so far in this field based on the detection theory for active pulse radars, but not for passive radars. Because of the major differences between active and passive radars, the detection methods used in active pulse radars are not applicable to passive radars and won’t lead to accurate results. So, in the current thesis, detection and target parameter extraction based on the detection theory have also been investigated and a method has been proposed. For this reason the passive radar hypothesis test is written and then parameters are estimated with GLRT for achievement of detection statistic. Finally, different methods of detection in passive radars have been compared using simulation to show the efficiency of the suggested method. Keywords: Passive Radar, Cancellation, Detection Theory, FM Radio Signal