| The Passive Bistatic Radar could utilize FM radio signals or TV signals to detect and track targets by receiving and processing the echoes from moving targets. And the radar does not need to transmit signals itself. Many counties are more and more interested in such passive radar system, because of its superiorities, such as favorable concealment, excellent counter-interference performance and powerful survival ability. But the echoes received by the radar are extremely weak, how to detect and track weak targets effectively becomes a difficult problem.This paper focuses on the weak targets detection of passive radar based on opportunity transmitter by FM broadcast station. The techniques,such as removal of the direct signal and multi-path signals and the estimation of direction of arrival, are mainly studied.The main work of this paper comprises:1) The applicability of using the FM radio signals to detect and locate targets is analyzed. The possible intensity of the direct signal received by the radar is studied, and the effect of the distance between the transmitting station and the receiving station to the whole radar system is also researched.2) The adaptive filtering algorithms are used to suppress the direct signal in order to solve the problem that the target signals may be completely submerged in the direct signal. What’s more, the comparison of the rejection performance of four adaptive filtering algorithms is given, and their computational complexity is analyzed.3) A new idea of DOA estimation by using the signals with known waveform in the passive radar system is proposed. The DOA estimation performances of three algorithms in different situations which may be encountered in practice are deeply studied.The simulations are given to testify that these algorithms above could play a effective role in the passive radar system. By using the signal processing program given in this paper to process the measured data, the weak target is successfully detected and located. |
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