Wideband Radar Signal Processing

Wideband radars have many advantages over the narrowband radars, for instance, more information of the targets and environment, which can be used in imaging and mapping, additional reliable classification and recognition for the targets; stronger capability of target detection in clutter; more accurate measurements of the location and movement parameters of the targets; better electromagnetic compatibility and immunity to active and passive interference; low probability of interception and better secrecy of illumination; more flexible waveforms to match the targets and environments. So wideband radars have the potential to cope with the increasingly complex task and the battlefield environment, and become the trend of radar development. Research on the wideband radar signal processing is significant in both the theory and application.This dissertation is addressed on the wideband radar signal processing, and its scope covers the target detection, clutter suppression and target return coherent and cognitive tracking based on waveform agile on fly. The work of this dissertation can be surmmarized as the following five aspects:1. The target detection performances in noise of wideband and narrowband radar are analyzed and compared. Firstly, the radar equation and target radar cross section (RCS) of the wideband and narrowband radar are discussed; then three statistical models induced from the scattering of real targets are introduced: wideband nonfluctuating target, wideband Rayleigh target and wideband Ricean target; the detection probabilities of these three target models for wideband and narrowband radars are deduced, and we point out that the detection performance in noise of the wideband radar is determined by the tradeoff between the two opposite factors, that are the target RCS decrease of the target RCS and the increase of the integration loss; finally, we conclude that though the performance of the target detection in noise of wideband radars outperforms the narrowband radar under high signal-to-noise ratio (SNR) in theory, the cross-point of the two detection probability curves is too high, and the result is that the detection advantage of the wideband radar is meaningless for real targets.2. The problem of wideband radar target detection in Gaussian clutter by one pulse is researched. Firstly, the advantage and problem of detecting targets in clutter by wideband radar are discussed; several present algorithms are reviewed, additionally, their advantages and disadvantages are analyzed; then we point that the difficult of wideband radar detection is the absence of the knowledge about the spatial distribution of the target scattering centers in real applications; to overcome this difficulty we design a novel algorithm for wideband radar detection—order statistics based modified sequential testing (OSBMST); by theory analysis, simulations and actual target returns validations, we prove the OSBMST can achieve better and more robust performance than the present algorithms for sparse scattering target when the prior knowledge of the targets'scattering centers distribution is absent.3. The problem of wideband radar target detection in non-Gaussian clutter by the returns of multiple coherent pulses is researched. The precise and approximate models of wideband target return are introduced firstly; then the spherical invariant random vector (SIRV) model of non-Gaussian wideband clutter and the method of generation are presented; based on the target and clutter models we design the wideband radar generalized adaptive subspace detector based on the generalized likelihood ratio test (GLRT). The statistical properties of the detector are discussed completely and rigorously, and a high efficiency algorithm for the detector is designed. Additionally, the detector is expended to fit the wideband radar target with Doppler spread. Finally, the performances of the detector are verified by simulations. The results show that the detector we designed can integrate the target returns from multiple pulses coherently, and has much better performance than the present analogous detectors.4. The method of clutter suppression and targets return coherent integration based on subband processing is developed. Firstly, the necessity of analyzing the wideband returns into subbands by the oversampled filterbank is discussed based on the characters of the wideband target return and clutter, and then the method of filterbanks design is introduced; additionally, we show that the purpose of clutter suppression and coherent integration for wideband is to enhance the target impulse response in the returns to increase the reliability of the target recognition, rather than achieve higher signal-clutter-ratio as the narrowband radar; in the sequel, the optimal and suboptimal weights for clutter suppression and target enhancement in subband are designed. Finally, the validity of this method is proved by the results of simulations and actual returns processing.5. The problem of cognitive tracking by wideband radar is investigated. Firstly, the concept and properties of the target impulse response (TIR) are discussed and the wide sense stationary - uncorrelated scattering (WSS-US) model is introduced to describe the TIR and its dynamical model; the problem of optimal waveform design for tracking in time domain is researched, and its infeasibility is analyzed; then a suboptimal waveform designed method in frequency domain and its realization algorithm are proposed; additionally, according to the constant envelope requirement of the radar transmitter power amplifiers, two methods of constant-envelope waveform design in terms of given spectrum, namely, the stationary phase method and the iterative weight least square method are given; finally, we show that the method we proposed can decrease the estimation error for wideband radar tracking in some condition.