Study On Techniques For Target Detection And Imaging With Wideband And Narrowband Radar

Due to its all-weather, all day/night and long range, radar imaging technique can enhance radar's information acquisition capability greatly, thus exhibits great value in both civilian and military applications. It also provides strange change for target identification. At the same time, it is also a landmark for development of radar techniques. Inverse Synthetic Aperture Radar (ISAR) imaging technique is a main part of radar imaging technique. It may be applicated to image for air target, space target and ship target etc. Target detection is the principal problems for Inverse Synthetic Aperture Radar (ISAR) imaging. It is a very important step to detect target timely and exactly in ISAR applications. Target detection and imaging with wideband and narrowband radar are the primary content of this dissertation. It may be summarized as following five parts:1. The target velocity estimation for target tracking is firstly discussed. The real range of target from radar is acquired through the addition of the range of narrowband range gate (i.e. reference range for dechirp) and the envelope motion amount retrieving from the envelope alignment of wideband data, then the least square fit is applied to the real range, so that the velocity of the target is retrieved. Compared to the conventional narrowband velocity estimation method, the method which uses the wideband and narrowband data can obtain higher precision and smaller variation. At the same time, the envelopes of the wideband and the narrowband signal and the Doppler information of the narrowband signal are synthetized to obtain a higher precision velocity of the target.2. Two methods for the single target detection in the narrowband environment are proposed. By constructing the corresponding phase compensation function, the signal coherence can be achieved, and then the simple FFT operation can be taken to implement the target energy accumulation. The first method using Sparse Radon transform to obtain the target motion parameter, and the second method using the modified Keystone transform to achieve the target motion parameter. Through the simulation it can be seen that the methods can achieve the signal energy accumulation effectively and it is advantage for target detection.3. Two different methods are proposed for multi-target detection in the narrowband environment. The one is based on the signal separation and the other is based on the Clean technique. Both the methods can firstly achieve the signal coherence and then by FFT to detect target. But the former one need to separate the signal in the frequency domain, and the frequency modulation rate searching is required, so it may be applied to the high SNR condition. Whereas for the latter one due to the reason that the Keystone transform is not sensitive to SNR, so it may be applied to the lower SNR condition.4. The problem for target detection in the wideband environment is systematically studied. The characteristic of adjacent correlation of the wideband signal, i.e. decreasing order of the wideband echo signal, is applied, and then combining the time-chirp rate distribution and the second-order Keystone transform to achieve the correction of the range curve and range migration, and finally realize the signal energy accumulation detection for single target. Following for multi-target detection two methods are proposed. One is processed for a single range frequency cell; the other is processed for the result of adjacent correlation. Both the methods are adopted the Radon Ambiguity Transform (RAT), but due to the reason adjacent correction is applied in the latter one, the scatterer energy can be accumulated, so it is more advantage for target detection.5. A method which combines the Polynomial Fourier Transform (PFT) and Clean technique for Range-Instantaneous Doppler imaging Algorithm is proposed. The motion parameters of maneuvering target are firstly estimated and then they can be used for constructing a phase compensation function for target motion compensation, following for every range cell the PFT is applied to search the scatterer parameter, and then the Clean technique is used for multi-scatterer condition, so the RID imaging for every time can be obtained with the parameters estimated, and by introducing the definition of entropy a optimal time for RID imaging is presented. Moreover the relation of Doppler center frequency and the variation of frequency modulation rate is used for ISAR rotation angle estimation, and finally the scale for ISAR imaging can be achieved.