Research On Key Techoniques Of Missile-borne Wideband Radar Signal Processor

Wideband radars have been widely used in radar terminal guidance as the continuous development of radar technology. Due to the wider absolute wideband of the transmitted signal, wideband radars have the ability of high range resolution. Compared with narrowband radars, wideband radars have particular advantages on anti-jamming, anti-acquisition, accurate detection and imaging, high precision tracking, and object identification. In this thesis, the real-time target detection algorithms for missile-borne wideband radars and anti-chaff methods are studied based on a real radar signal processor with the background of anti-ship terminal guidance radar.The existing target detection methods for wideband coherent radars are usually complex and consume large amount of computation, therefore it is difficult to realize in real-time by missile-borne radar. For missile-borne radars, range migration of the target echoes during a coherent processing interval(CPI) is serious, which disperses the echo energy of the target and increases the difficulty of target detection. In the thesis, range alignment for target echoes is accomplished in the frequency domain during the process of digital pulse compression. Then a range-spread detection algorithm based on the waveform entropy(WE) of the average combination of high range resolution profiles(HRRP) is addressed, which has the property of constant false-alarm rate(CFAR). The target detection performance of the algorithm is assessed by Monte-Carlo simulation, and the result indicates that the detection performance of the proposed detector is superior to the traditional energy integrator and is robust for HRRPs of the target. For the problem of range and Doppler distributed target detection, a novel double thresholds target detector based on the range-Doppler image is proposed. The range-Doppler image of the target is derived and analyzed, and then the clutter cells are removed and the range-Doppler image is obtained by the first threshold. The detection statistic is constructed by the energy integration of the estimated range-Doppler image and the detection result is obtained by the second threshold. The simulation results indicate that the target detection method based on the range-Doppler image is superior to the direct energy detector and the binary integration detector. In addition, the proposed target detection method is robust and easy to implement.Frequency stepped chirp radar(FSCR) can achieve high range resolution while still retaining the advantages of lower instantaneous receiver bandwidth and lower analog-to- digital(AD) sampling rate, and is widely used as a kind of wideband radar in recently years. FSCR achieves high range resolution by synthetic wide-band technique, and the process includes intra-pulse matched filtering and pulse-to-pulse IDFT or wavelet transform. For FSCR, the HRRP of the target is obtained by target extraction from overlapping HRRPs which is caused by oversampling. During the target extraction(sometimes called de-correlation), some strong scattering points of target echo are discarded, as the result, the signal-to-clutter ratio(SCR) might be reduced and the target detection capability is degraded. To solve this problem, a novel detection algorithm without target extraction is proposed. The new algorithm based on the power spectrum of radar echo uses not only the amplitude information, but also the phase information of overlapping HRRPs of a target to improve the SCR, therefore, has significant performance. The detection performance is assessed by Monte-Carlo simulation, and the results indicate that the proposed detector has significant improvement in SCR compared with the SSD-GRLT detector and the energy integration detector.For missile-borne FSCR, the range migration of target echo during a coherent processing interval, resulting from the high speed motion of missile, is serious and will affect target detection and synthetic of the high range resolution profile. Therefore, range migration correction and motion compensation are very important for missile-borne FSCR signal processing. In the thesis, with the background of terminal guidance anti-ship FSCR seeker, the range alignment is accomplished in frequency domain during the process of real-time digital pulse compression. Then an effective velocity estimation algorithm based on the waveform entropy of the Doppler amplitude spectrum of target echoes is addressed and the velocity estimation accuracy is derived. The simulation indicates that the velocity estimation method can estimate the radial velocity accurately and reconstruct the distorted HRRP successfully. In addition, the method has good anti-noise performance and is easy to implement.Among the defensive measures against anti-ship missiles, chaff is probably the oldest, but still an effective measure. Besides, comparing to other countermeasures, chaff is inexpensive and easy to use. Consequently, it is widely used by Naval Force all the same. Anti-chaff jamming technology has gained much attention among radar engineers in the past decades. Due to the working environment, however, anti-chaff jamming performance of the missile-borne terminal guidance radar is still imperfect ever since. Wideband radar has the ability of high range resolution, which provides us a new technological approach for anti-chaff jamming. In addition, the coherent radar is usually adopted to restrict clutter and jamming echoes by Doppler analysis. To study effective anti-chaff jamming methods, the thesis investigates the echo characteristics of the vessel and the chaff for wideband coherent radars, and proposes an effective anti-chaff method based on the range-Doppler image.Based on the measured data, the differences of the echoes between the vessel and the chaff are analyzed. Then in terms of the spread feature and the energy evenness of the range-Doppler image, two features of the radar echoes are proposed to distinguish the vessel and the chaff, and then the statistical distributions of the two features are investigated. Based on the two proposed features, the anti-chaff method is designed and the experiment results by the measured data indicate that the method is effective.Finally, a real wideband radar signal processor is designed and implemented. Radar signal processor is a key part for radar seeker. In this work, we propose and assess a miniaturized signal processor for missile-borne wideband monopulse radar. To improve the commonality and expansibility of the signal processor, the FPGA+DSP structure is adopted in signal processor design. Based on the structure of the target detection algorithms and the anti-chaff method proposed above, the hardware realization of the signal processor is presented. Finally, some measurements and compensation for the monopulse radar signal processor are implemented, and the experiment results indicate that the design of the signal processor is successful.