Research Of Waveform Diversity In Adaptive Radar System

As an important diversity, waveform diversity (WD) technique has been an important development direction of the modern radar system. With this new diversity technique, the performance of detection, tracking and anti-jamming of radar can be optimized by altering its transmitted waveform, and at the same time it's difficult for enemy to perform electronic reconnaissance and jamming. The theory investigation of WD in adaptive radar system is of much theoretical and applicable significance in the exploitation of adaptive radar system and the improvement of the performance and anti-interference ability in future battlefield.In this thesis the theory and method of WD in adaptive radar system are investigated and main works are accomplished as follows:Firstly, basic principle of optimum matched illumination and reception is analyzed for the adaptive operation mode of alternative search and detection for radar. Extraction of multiple scattering points of the target and design method of optimum matched illumination transmitted waveform and the correspondence receiver are investigated based on phase-coded radar signal. It is considered that the apriori information obtained by recursive function can be used to adaptively suppress range sidelobes. An adaptive range sidelobe suppression algorithm based on recursive maximum signal-to-noise ratio (SNR) criteria is presented. Every scattering point of the target can be extracted reliably and complex amplitude of the scattering point can be accurately estimated. The accuate target model with multiple scattering points can be constructed. The matched illumination phase-coded signal design method based on conjugate gradient algorithm in phase domain is also investigated. The phase-coded radar signal derived by this algorithm approaches the optimum matched illumination signal and this algorithm enjoys fast convergence and small computation amount. The results show that matched illumination not only increases the SNR of the matched filter output, but also decreases the variation of the output SNR at different attitude of the target. Better and more stable detection performance can be obtained by adaptive radar system and this conclusion can be used for adaptive radar system design in future.Secondly, anti-jamming technique based on WD for countering active jamming, especially the narrow-band interference (NBI) and deception jamming, is studied. With the apioror information of the NBIs from other electronic systems, a new kind of phase-coded signal design method which minimizes the power spectrum in bands of the interference and the correspondence frequency domain processing method are proposed for foliage penetration ultra wide band radar (FOPEN UWBR). The synthesized signal has the approximatly ideal power spectrum and good range resolution and high peak sidelobe ratio (PSLR) after frequency domain mismatch processing. For target detection under deception jamming of range gate pull off (RGPO), a set of specified transmitted signals orthogonal in frequency and the correspondence processing method are presented to eliminate the jammer signal which is a copy of the transmitted radar signal. This method improves the target tracking and multiple target detection performance by WD. For target detection under synchronous range and velocity jamming, a novel anti-jamming method of removing deceiving decoys based on transmitted signals with adaptive random initial phases is studied. Adaptive random initial phases which can form a notch covering the Doppler frequency of the target make detection unaffected. The multi-channel auto correlation processing method is given to extract the manner the jammer operates and the parameters of the false targets. Work flow of a pulse Doppler radar is also designed. The simulation results show the anti-jaming capability of radar by itself for countering high power jamming.Thirdly, to optimize adaptive multiple-input multiple output (MIMO) radar performance, colocated and bistatic MIMO radar are studied based on ambiguity function. Range and spatial resolution of the collocated MIMO radar is given. It is shown that the peak value of the matched filter is affected by the difference of the real target and assumed spatial frequency and the sidelobe is determined by the real target and assumed spatial frequency. According to this property, an algorithm for adaptively designing orthogonal frequency-hopping waveforms according to the target spatial frequency is proposed. The search spatial region is divided into multiple sections by spatial resolution and waveforms are optimized to improve the peak sidelobe level (PSL) of the matched filter output for for the collocated MIMO radar. Characteristic of range-velocity ambiguity functioin of the bistatic MIMO radar is also analyzed, and range and velocity resolution of bistatic MIMO radar are deduced. An algorithm for adaptively designing orthogonal waveforms according to the target position is proposed. This algorithm jointly optimize the code width, the number of the code and code set of the frequency code waveforms and improves the range and velocity resolution and the integrated sidelobe level (ISL) of the matched filter output at the correspondence position. This method sloves the problem that the range and velocity resolution decreases with the increased bistatic angle, and can also be applied in performance optimization for multistatic and netted radar systems.Finally, transmit beamforming and matched filter beamforming are studied for MIMO radar based on modern optimization theory. The adaptive transmit beampattern design for MIMO radar is converted to a semi definite second order cone programming model. The cross-correlation matrix optimization method based on modern convex optimization theory is proposed. Simulation results show the synthesized beampattern can keep the main beam shape and minimize the sidelobe in specified angle section. Digitial multi-beam forming in MIMO radar receiver is also studied. A new matched filter beamforming model is proposed. In this model, the transmitter and receiver can be designed simultaneously by jointly optimizing the cross-correlation matrix of the transmitted signals and the beamformer, therefore greatly increasing the freedom degrees of MIMO radar system. The penalty fuction for multi-beam forming optimization design is built and the correspondence optimization method is given. Simulation results show that this method can obtain better beampattern than that derived by the original matched filter beamforming model.