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Research On Key Technologies Of FM-CW Synthetic Aperture Radar Signal Processing

Posted on:2009-04-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:S M GengFull Text:PDF
GTID:1118360242499392Subject:Information and Communication Engineering
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The combination of frequency modulated continuous wave(FM-CW) technology with synthetic aperture radar(SAR) methods should pave the way for the development of a small, lightweight, cost effective imaging sensors of high resolution. Mini-UAVs (MUAV) have reached a high degree of maturity; however, so far these platforms' major drawback is their limited payload. The highly miniaturized FM-CW SAR system satisfies the requirement of cost-effective development trend and it's small enough to be mounted on such MUAV system for its advantages such as compact, cost-effective, low power consuming and low probability of interception (LPI), etc. So, more and more scientific research organizations show a great interest in it. In this dissertation, the challenge technologies of FM-CW SAR in theory and practice are discussed.The stop and go approximation is the basis of pulse SAR processing and theoretic analysis, however, in FM-CW SAR applications, the conventional stop and go approximation used in pulse radar algorithms can be not valid anymore for its relatively long sweep cycle. The thesis firstly analyzed the effectiveness criterion of the approximation; then analytical development of FM-CW SAR signal model is presented without using the stop and go approximation; in addition, according to the given signal model, a fast raw data simulation algorithm based on FFT is presented.Residual Video Phase (RVP) and the slope factor are the characteristics of the De-chirp operation, the thesis analyzed their effects on conventional SAR imaging quality, and the corresponding compensation methods are discussed. The carrier's motion within the sweep causes the fast-time Doppler effect, based on the Range-Doppler algorithm, the thesis discussed the range walk caused by fast-time Doppler effect and the correction method is given. In the case of large beam width, a modified Range-Doppler algorithm is proposed to conquer the performance deterioration caused by the model approximation.The Range-Doppler algorithm correct the fast-time Doppler effect in azimuth Doppler domain by interpolation, the compensation precision is restricted by the interpolation precision. To conquer this problem, the thesis proposed a modified Range Stacking algorithm. The algorithm does not require interpolation, no existing the geometry distortion, its reconstructed images do not suffer the precision loss from interpolation calculation; it is applicable in near-field FM-CW radar imaging.Another outstanding problem in FM-CW SAR system is that the sampling frequency and the data processing capacity are limited. In the case of low sampling frequency, the frequency spectrum in range may badly be folded if the conventional pulse SAR FS algorithm is used in FM-CW SAR directly, the imaging quality is deteriorated. To solve the problem, a modified FS algorithm is proposed, which avoided frequency spectrum fold in range caused by scaling transform, as well as corrected the range walk caused by the motion during the sweep and range curvature caused by the motion between successive sweeps, the precise imaging is accessed.Moving targets indication (MTI) based on airborne radar systems has been a crucial function for military application. To maintain the advantages like small, light weight, etc. and make the best of the single antenna of FM-CW SAR system, users hope that MTI is implemented using one single channel echo data. The thesis combined the ideal of constructing the double channels returns by transmitting linear triangular wave for reference with the DPCA method, proposed a new algorithm on single channel MTI. The algorithm investigated on emphasis that the RVP which can be ignored in the stationary targets imaging may cause severe phase mismatching between the two channels, and drew the conclusion that, to get better SCR, the RVP must be eliminated in the imaging process.Finally, in terms of system design, the thesis analyzed the key elements limiting the system performance—frequency modulation (FM) nonlinearities and the phase noise. By the quantitative analysis on relation between linearity and PSLR, the linearity-PSLR curve is gotten by data approximation, and then the linearity requirement of the signal source is gotten easily by the anticipant PSLR. Furthermore, the thesis discussed the effect of the phase noise of oscillator and the leakage signal, and got the formulation of FM-CW SAR image CNR, which is used to guide the Engineering Practice.
Keywords/Search Tags:Synthetic Aperture Radar(SAR), Frequency Modulated Continuous Wave(FM-CW), De-chirp, Imaging Algorithm, Range Doppler(RD) Algorithm, Range Stacking(RS) Algorithm, Frequency Scaling(FS) Algorithm, Fast-time Doppler Effect, Amplified-RVP(ARVP)
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