Research On The Principles Of Direct Demodulation And Technology Of Real-time Pulse Compression In Wideband Radar

The linear frequency modulation (LFM) signal with high time-bandwidth (TB) product is mainly used in the wideband characteristics measurement radar. The dechirping processing which need a low sampling rate is severely restricted in the application range because of the rectangular window, but the problem can be avoided in direct receiving processing. Aiming at the implementation issues in the direct receiving channel of the wideband radar, on the background of the development of the X-band characteristics measurement radar with the bandwidth of 1GHz, the demodulation to obtaining the digital in-phase/quadrature (I/Q) components with high precision and the real-time pulse compression are studied in this thesis. And the main contributions are shown as follows:1. Aiming at the larger demodulation error in the traditional analog quadrature demodulation topology of wideband radar, the Double-IF sampling digital I/Q demodulation model with the self-correction function of demodulation error is put forward, and the dependence of 90-degree power divider can be avoided in the model. Aming at the rapid implement of the model, two fast reconstruction algorithms of digital I/Q signal are studied, and the corresponding direct demodulation topologies with Double-IF sampling which can be easy to self-correcte the demodulation error and greatly reduce the computational are designed. The simulation experiment gives that the topologies can improve about 15dB in the image rejection ratio (IRR) under the signal bandwidth above GHz when compared to the traditional analog quadrature demodulation topology.2. Aiming at the implementation issues of the less selection of center frequency and the sampling rate of the intermediate frequency (IF) signals and not conducive to the front-end engineering design in the digital quadrature demodulation topology, the mixer-free equivalent complexsampling method based on second-order sampling is proposed. The selection of center frequency and the sampling rate is greatly expanded and the difficulty of the front-end engineering design is reduced.3. Aiming at the implementation issues of the high requirements of sampling rate and filter order and the large computation in the digital quadrature demodulation topology of wideband radar, two sampling time difference eliminating methods called the shifted unit impulse response method and the improved shifted unit impulse response method by the frequency-shaping are proposed. The two methods have the advantages of avoiding the sampling time difference eliminating filter and reducing requirements of the sampling rate and the computation. The improved shifted unit impulse response method by the frequency-shaping also has a higher IRR and can process the complex exponential signal with arbitrary center frequency directly when combined with the shifted unit impulse response method. The corresponding direct demodulation topologies with Single-IF sampling which are more suitable for wideband radar than the traditional digital quadrature demodulation topology are designed.4. Aiming at the implementation issues of large computation and the poor real-time processing in the large TB signal, the novel fast algorithm pulse compression method is proposed. The corresponding process flow sheets and the parallel processing projects in frequency domain which can reduce the computational redundancy and computation and improve the real-time performance are presented.Finally, the system based on direct demodulation and real-time pulse compression is designed and manufactured when combined with the X-band characteristics measurement radar with the bandwidth of 1GHz. The system which can expand the imaging capability of high range resolution profiles from a few hundred meters in dechirping processing to 5km.