Research On Key Technique Of Passive Radar Based On External Illumination Signals

Modern warfare can be charged in the time domain as the implementation of thestrategy, planning, game and evaluation process, and to control the land, sea, air andspace areas in the airspace domain. It is very important to collect the information andprocess and then application, no matter in time or spatial domain. With the rapiddevelopment of high-tech weapons and equipments, how to get the target’sinformation becomes the key point of both sides. In a sense, modern warfare is justinformation warfare. Militarv radars is the sensor to get the targets’ information, theycarry on the target detection, location, tracking, classification, recognition, imaging,alarm and transmission, and they are of great significance. However, with thedevelopment of anti-radar technologies, any military radar will face the four bigthreats, that is stealth, anti-radiation to destroy, penetration with low altitude andcomprehensive electronic jamming and so on.Passive radar, which is based on the opportunity illuminators, uses multichannelin different regions in the way of spatial diversity to receipt and deal with stealthytargets’ non-backscatter energy so as to achieve the aim of anti-stealth; Takes theopportunity illuminators as the transmitted signal, then anti-radiation missile cannotfind the goal; Adoptes MIMO system and bistatic angle which are useful forimproving detection performance at low altitude; Uses interference sources signal,so multi-station or single-station reception can be effective to locate and track theinterference sources. According to the above reasons, passive radar causeswidespread concern. In this paper, GSM or DVB-T is used as opportunityilluminators, and feasibility of the system, structure of the system and theoreticalalgorithms are discussed deeply. The main contents are specifically embodied in thefollowing aspects:(1) Propose adaptive beamforming method based on blocking signal to extractthe direct wave.Reference signal is very important for coherent detection in passive radarsystem, which directly affects target detection performance. Only use the common beam forming may obtain impure signal, while directly use the adaptive beamforming may not get the direct wave signal from the main base station. This paperproposes an adaptive beam forming method based on blocking signals to form themain lobe at the direction of the main base’s direct wave, simultaneously to formnull at the direction of the relatively strong interference. Firstly, eliminate the mainarray antenna base station receiving the signal of the direct wave signal eliminationthe direct wave signal of base station, then use adaptive beam forming algorithm toobtain the optimal beam forming weight, last to use beam form to get the direct waveof the main base station. The effectiveness of the proposed method is verified bysimulation data, and then analysised using the measured data. Compared with theconventional LCMV adaptive beamforming method, the proposed method is moresuitable for the application in engineering.(2) The interference suppression method of passive radar by doing Time-domaincancellation before beamforming is proposed.External illuminator based passive radar is a variation of bistatic radar thatexploits non-cooperative illuminators of opportunity as its radar transmitters, Thereceiver is able to receive not only the transmit signal to the primary base station butalso other nearby base stations transmit signals in the same frequency interferenceand multipath interference, Simultaneously affected by environmental noise. In thispaper, a new method is proposed that first usingtime domain interferencecancellation algorithmto eliminate each array element antenna array in the main basestation receiving the direct wave and multipath interference and thenundertakingrobust adaptive beamformingfor each antenna array element residual signal. For theinterference of the wave from main base stations and multipath interference havebeen eliminated based time-domain interference cancellation algorithms, adaptivebeamforming antenna will be all degrees of freedom in suppressing interference basestation on the same frequency. Therefore, it is able to get well effect of co-channelinterference suppression effect on airspace. As the real environments are with muchnoise, the denoising method based on choosing proper reconstructed waveletthresholding is undertaken. In this method, the Haar wavelets are chosen and thesignals are through three decomposition. In order to improve the effect ofsuppressing clutter, denoising thresholds are set according to the characteristics of each layer signal.(3) Passive bistatic radar clutter channel estimation based on pilot signalextraction.This paper proposes a clutter channel state information estimation method forOFDM (orthogonal frequency division multiplexing) modulation-based passivebistatic radar. First the concept of OFDM signal characteristics-based targetdetection is advocated for the detection problems in OFDM-based illuminator. Thenfor the training information isn’t directly available for passive radar application,ambiguity function for OFDM Pilots period, then pilot locations estimation are given.After pilot locations are known, channel impulse response information can beobtained by using the pilots’ information. Compared to the conventional passiveradar processing method, the proposed method can quickly realize the clutterchannel state information estimation in the case of the reference signal composingmultipath clutters.(4) Tracking algorithm based on MCMC-optimized particle filter is proposed.In target localizationof external illuminator based passive radar,measuredparameters are direction of arrival、 time difference of arrival anddopplerfrequency,so the common positioning methods are DOA、TDOA、FDOA andjoint positioning by different combinations of thethree measured parameters. In thisdissertation,based on GSM external illuminator,wechoosedthe joint location of DOAand TDOA. In target tracking,this paper studied target tracking algorithm based onMCMC particle filterand target tracking based on optimized particle filteras theproblem of particles degradationin target localization of external illuminator basedpassive radar.The performances of twoalgorithmsmake a comparison and proposedMCMC-optimized particle filtertracking algorithm which conbinethe advantages ofboth.In a certain extent, the problem of particle diversity loss is solvedand theaccuracy of trackingis improved.(5) Passive radar ISAR imaging based on multiband DVB-T signal andTime-Frequency analysis.Since the move of object results in the change of scatterers’ echo Dopplerfrequency, so that ISAR images blur. Conventional method of radar imaging takes agreat effort to do echo distance alignment and phase alignment. This paper chose the multiband DVB-T signal to obtain non-adjacent channel signals to extend signalband so that the bandwidth can be wide enough to get sufficiently high resolution.And this paper proposes the use of time-frequency analysis method which can avoidcomplex motion compensation. As long as the distance aligned, Doppler frequencycan be considered to be constant, which reduces the dependence of the motioncompensation. What’s more, for the case of noisy environment, based on thetime-frequency analysis, use CLEAN algorithm to extract the location informationof Scatterers. Experimental results demonstrate the effectiveness of this STFT+CLEAN algorithm method.