Study On Some Issues Of Signal Processing For Passive Bistatic Radar

Passive bistatic radar (PBR) itself doesn’t transmit electromagnetic wave. It detects,locates and tracks target relying on the external illuminators which have already existedin the environment. Because of the property of passive detection, PBR has an excellentcapability of anti-interference and good survivance. In addition, relying on its bistaticgeometry and signal characteristic of illuminator, PBR has an excellent capability todetect low altitude targets and stealth targets. Therefore PBR is the new type of radarwhich has bright application value.This dissertation addresses some aspects of signal processing for PBR. Theresearch focus on direction of arriving (DOA) estimation for frequency modulated (FM)based PBR, mismatched filter for analogue television (TV) based PBR, interferencesuppression for cell mobile communication based PBR.The main contents of this dissertation are summarized as follows:1. A method of single target’s DOA estimation based on Adcock antenna isstudied. First temporal adaptive cancellation is utilized to remove the interferences fromeach elements of Adcock antenna, and then range-Doppler two-dimension (2D)correlation between the remained signal from each channel and reference signal isutilized to improve signal noise ratio (SNR) of target. Finally target’s DOA is estimatedin the range-Doppler bin corresponding to the target via a method based onphase-comparison principle. This method can measure target’s DOA in the range of360°without ambiguity. When there are several target echoes received by the antenna,the sidelobe of strong target echoes may affect the DOA estimation of weak targets. It isproposed that the DOA of strong targets can be first measured. Then after removing thestrong targets, the DOA of weak targets can be estimated in the end.2. A method of multiple targets’ DOA estimation based on compressed sensing isintroduced. First when there are several target echoes received by the antenna and twoor more targets are included in a same range-Doppler bin, the signal model in this bin,after temporal adaptive cancellation and range-Doppler2D correlation, is acquired. It ispointed that the signals in this bin can be seen as the linear combination of noise andmainlobe of the targets corresponding to this bin. So if the number of array elements islarge enough to make the signal in the bin spares in space, the signals of this targets’range-Doppler bin can be reconstructed according to DOA using spares reconstructionalgorithm of compressed sensing. Then all the targets’ DOA belonging to this bin can beacquired. The performances of the proposed method are verified by simulation experiments in the end.3. The technique of analogue TV signals based mismatched filter is studied inthe fourth chapter. At first, the characters of ambiguity function of visual and audiosignal are analyzed separately. It is pointed that although the audio signal has theidealized thumb-tack ambiguity function which is very fit for PBR, its transmittedpower is low. Whereas although the transmitted power of visual signal is high, it hasrange ambiguity. In order to solve the range ambiguity of visual signal, a method ofmismatched filter based on only visual signal is introduced. Simulation results showsthat after mismatched filter, the ambiguity range sidelobe can be suppressed, but there isa large SNR loss. In the end, a mismatched filter based on both visual and audio signalis proposed. Simulation results show that the proposed method can not only utilize allthe transmitted power of analogue TV but also suppress the ambiguity range sidelobewith lower SNR loss comparing to use only visual signal.4. An interference suppression method for global system for mobilecommunication (GSM) based PBR using two-step spatial filter is introduced. In GSMbased PBR, there are not only strong interferences but also a lot number of weakinterferences. In order to suppress all interferences in GSM based PBR, it is proposedthat the weak interferences can be first suppressed using low sidelobe spatial filter, andthen the remained strong interferences are further suppressed by a robust adaptivebeamformer. Simulation results show that, compared to adopt only low sidelobetechnique or robust adaptive beamformer, the proposed method can suppress theinterferences in GSM based PBR better.5. A method of interference suppression based on concatenation cancellation forcode division multiple access (CDAM) based PBR is given. In order to suppress all ofthe interferences from each CDMA base station, first pilot search is utilized to identifythe pseudonoise (PN) offset of the strongest direct signal. Then the DOA of thestrongest direct signal is estimated. After acquiring the strongest direct signal, theinterferences from this base station are removed using a temporal adaptive cancellationalgorithm. Repeat this in turn according to the energy intensity of each CDMA basestation till all the interferences are suppressed sufficiently. Simulation results verify theefficiency of the proposed method in the end.