The Parameters Estimation And Sorting Of LPI Radar Signals Based On Digital Channelized Receiver

It presented new challenges to the modern passive investigation receiver and anti-radiation missile seeker with the appearance of low probability of intercept (LPI) radar. Pulse compression radar is a kind of LPI radar. This kind of radar can compress the return long pulse into a short one. The pulse compress technology can reduce the probability of intercept. Also, it can improve radar's range resolution. The traditional receiver can't receive this kind of radar signals, so, the wide-band digital receiver which can store frequency and phase information must be developed. As a mature wide-band digital receiver system, the digital channelized receiver can achieve "blind receiver" to different system radar signals.The pulse compression radar signal modulation parameters can be extracted by using modern signal processing algorithms, once the signals are intercepted. Phase shift keying (PSK) signals and frequency modulation (FM) signals are two kinds of widely used pulse compression signals. The PSK signals include binary phase shift keying (BPSK) signals and quadrature phase shift keying (QPSK) signals. Linear frequency modulation (LFM) and non-linear frequency modulation (NLFM) signals are the kinds of FM signals. To achieve parameters estimation of PSK, the carrier frequency, coding sequence and code rate must be extrated. The LFM signals parameters which need to be extracted include the initial frequency, the end frequency and the chirp rate. For processing to the non-linear FM signal, the phase polynomial coefficients must be estimated.In the signals sorting, the steps are that, at first, achieve pre-sorting by using the signal parameters obtained from digital channelized receiver, then, remove the radar signals which don't meet the requirements to achieve the purpose of diluting pulse flow, at last, in the main sorting, the pulse repetition interval of pulse train was calculated by the arrival time of a single pulse.The pulse compression radar signals were intercepted and identificated in digital channelized receiver. In the paper, the parameter estimation algorithms of PSK and FM signals were researched in deep, and the signal sorting algorithms were discussed in detail.The derivation of high-speed and efficient structure of the uniform digital channelized receiver based on polyphase filter and FFT was given in the paper. For processing of channelized subsequent, CORDIC algorithm was adopted to extract instantaneous amplitude and phase of signals. The output of the zero channel is real, to this question, a method called complex processing to the zero channel based on Hilbert transform was proposed. In the terms of signal parameters estimation, at first, the spectral analysis can be used to complete pulse modulation classification. The cyclic autocorrelation can achieve recognition to PSK signals, this method can distinguish between BPSK and QPSK signals, to extract this kind of signal parameters, a method called integral-envelope has been proposed, combined with the carrier frequency, the subcode width and coding rule can be estimated. This algorithm can also estimate the chirp-rate, initial and terminal frequency of LFM signals. The method called cubic phase function (CPF) can be used to achieve parameters estimation of LFM and NLFM signals, this method can extract the phase function coefficients. The computation of this algorithm is very big, for this question, the search range criteria was proposed, in addition, a method called dual-scale search of frequency slope was brought forward to reduce the computation, also, this method can maintain the accuracy of the algorithm.In the terms of signals sorting, To solve the problems that the traditional methods can't effectively sort high-density and complex radar-signals, and the existing clustering methods can't achieve real-time requirement. A new method of sorting radar-signals based on modified fuzzy clustering by using radar-pulse parameters has been proposed. In this modified algorithm, the concept of distance weighted coefficient was put forward, it's more reasonable to determine the distance weighted coefficients of the parameters based on information entropy. By using the tracking method to calculate the equivalent fuzzy matrix and get the serial number of the pulses has more practical significance. The modified PRI algorithm can be used to calculate the PRI of signal. In the hardware, a method called non-uniform setting PRI-box width was proposed, it can save much algorithm running time to enhance the system real-time performance. This sorting method solved the sub-harmonic problem in the past histogram statistical method and overcame shortcomings existed in the traditional PRI algorithm which can't effectively sort jitter pulse trains.