Research On Parameter Estimation And ISAR Imaging For Distributed Coherent Radar

With the rapid development of aerospace technogy, the rivalship is getting moredrastic in the space environment. Space and aeronautics incorporation has become animportant trend for the worldwide revolution in military affairs. Therefore, the surveillanceof space targets is quite critical in the space attack-defense confrontation. Distributedcoherent radar is the state-of-the-art technology for space surveillance with the advantagesof long radar detection range, high space and time resolution, transportable capability, easyrealization and reduced cost. Although some experiments have been demonstrated for theability of radar coherent, it is still on the initial stage of development and there remainmany problems to be resolved.The distributed coherent radar investigated in the dessertitation adoptsstepped-frequency signal as the basic transmitted waveform. The transmitters are deployedconcentratedly for the cohere-on-transmit realization while the recerivers are deployeddistributedly for high-resolution ISAR image formation. Based on this type of distributedcoherent radar, this dissertation makes a fully investigation on radar coherent and ISARimage formation. The general content of this dissertation is summrised as follows:1. Signal modeling and coherent performance analysis of distributed radar based onstepped-frequency signal is studied. The signal models are initially established for fullcoherent distributed radar based on stepped-frequency signal including parameterestimate model for cohere-on-receiver mode and signal error model forcohere-on-transmitter mode. Based on parameter estimate model, Cramer-Rao lowbound is elaborately derived and it is figured out stepped-frequenncy signal isappropriate for high-accuracy parameter estimation. Meanwhile, Based on signal errormodel, the estimate accuracy of coherent parameter is analysed for thecohere-on-transmitter under stepped-frequency signal waveform. In addition, thelimitation of radar deployment is also analysed for the cohere-on-transmit realization.Finally, the demand of estimate accuracy on signal-noise ratio (SNR) is investigated. Itis of great significance for the design and realization of distributed coherent radar.2. Coherent parameter estimation of stepped-frequency-signal distributed coherent radaris studied. Firstly, the high resolution profile reconstruction for stepped-frequencysignal is modeled and two methods are proposed based on the back projection and least squares estimate, respectively. Meanwhile, the unambiguous restriction of these twomethods on stepped frequency is analysed and also validated by the simulations. Inaddition, the model of coherent parameter estimation is established in the case ofmultiple-input-multiple-output (MIMO). For coherent time estimate, a fast itetationcorrelation method based on range-profile entropy. For coherent phase estimate, therough estimation based on the profile correlation and fine search based on thesharpness criterion are combined, where both entropy and contrast are used for the finesearch. Finally, the proposed estimate methods are validated with respect to bothefficiency and accuracy by the simulations. It could lay a solid foundation for thecohere-on-transmit mode and further distributed ISAR imaging.3. High-resolution image formation method for distributed coherent ISAR is investigatedbased on image entropy. A general distributed ISAR signal model is firstly estabilishedand the mapping between bistatic SAR imaging plane and echo data is obtained. Then,aim to address the translational motion compensation problem of range alignment andphase adjustment, the image optimization function of entropy is adopted and aquadratic approaching method is proposed, where the range alignment method adopts acascade filtering processing to avoid the convergence at the local optimization. Bothsimulational and real data are used to validate the accuracy and robustness of thepresented compensation method. Next, an estimation method of imaging planeconsisting of rotational center and velocity is proposed to obtain the mapping of echodata of separate receivers into the indentical space coordinate. Thus, the separate ISARimages in the same coordinate can be reconstructed based on the method of backprojection. Futher, the coherent phase of receivers can also be estimated and then theseISAR images can be perfectly fused. Finally, the effectiveness of the proposed methodis validated by the simulation, which suggests the proposed method could provide thehigh resolution information for target recognition.