Study Of The Detection Of Weak Targets Of The Passive Radar Based On The FM Broadcast

Many countries show considerable interest in the passive radar systems based on the transmitter of opportunity, because of its particularities, such as anti-stealth ability, anti-reconnaissance ability and subsistent ability. Such systems utilize the signals emitted by broadcast station, TV station and secondary planet. The targets such as stealth aircrafts and cruise missiles can be detected by correlation detection. The DOA (Direction Of Arrival), TOA (Time Of Arrival)and Doppler shift can be estimated, and then the targets can be tracked and identified. Such systems don't emit electromagnetic waves as conventional radar systems do and the frequency of the commercial broadcast lies in VHF band. So that systems have the advantages of good subsistent ability and good anti-stealth ability, besides the advantages of the conventional radar systems. Recent experiments on the passive radars have proved that the passive radar systems are promising as a supplement to the conventional detection techniques. Such systems keep themselves in the foreground and can be utilized in many civil and military fields. As to the important problem that how to choose opportunity transmitter, John (America)'s study indicates that FM broadcast signal's correlation time is shorter than that of other opportunity signals and that signals are approximately white noise, when the time lag is longer than 1ms. So the FM signals as an opportunity signals have the advantages of good performance of impulse compress, low system error of receiver and easy access. Chadwick's study indicates that in such system the key technique is to detect weak radar targets with strong direct path signal. The primary contributions and original ideas included in this dissertation are summarized as blow:1. The applicable signal-processing scheme is systemically developed. That the precondition of good detection ability is good performance of clutter suppressor is also pointed. The relation between correlation coefficient and the clutter suppression ratio is presented. The influence of the sampling frequency on the suppression ratio is also studied. The algorithms of clutter suppression and weak signal detection are presented, based on the estimation of the time delay of fractionally spaced clutters. Such algorithms make use of the high resolution of the time delay estimation. The algorithms transform the demand on sampling frequency and length of clutter suppression filter to the demand on TOA estimation precision of the direct path signals and multi-path...