Study On Waveform Design And Imaging Technology For Formation-flying Satellites SAR

Formation-flying satellites SAR has drawn extensive attention in recent years andis becoming the hot research field in radar technologies, due to their properties ofhigh-resolution, wide-swath, three-dimensional imaging and GMTI(Ground MovingTarget Indication). In order to realize high-resolution imaging, there are lots of keyissues for formation-flying satellite SAR. First, the orthogonal waveforms must beguaranteed，because there is serouse interference between the transmitting beams due tothe overlap of the irradiation areas for the formation-flying satellites. Secondly, thequality of SAR image decgrades dramatically caused by the movements of the satellite.Thus, the movement compensation is required for formation-flying satellites SARsystem.. Besides, with the inhencement echoes, the transmitting payloads of thesatellites are increasing grealty, they aggravate the burden of the satellites transmission.In order to solve the problem, the sparse method of formation-flying satellites SARechoes and the imaging method of formation-flying satellites SAR are studied. Themain works of this derstation are summarized as follows:1. The Hybrid-LFM waveform is proposed by modulating the slope of LFMsignal. The influences of orthogonal performance and doppler tolerance for thedifference of frequency modulation slope are analyzed, and the relationship between theparameters of the waveform can be deduced. Two kind of waveform parameter designmethods are proposed, and the Hybrid-LFM waveform with good orthogonalperformance and good doppler tolerance are designed.2. The OCD-LFM waveform is proposed by modulating the orthogonal phasecode to the phase of LFM signal. The influences of orthogonal performance and dopplertolerance with different length of phase code are analyzed, the relationship between theparameters that minimize the cross-correlation peaks and minimize the effect of dopplerfrequency shift of the proposed signals is derived. The waveform optimization methodbased on genetic algorithm is proposed.3. The yaw steering method of formation-flying satellites SAR based on the scenecenter offset is proposed, and the doppler centroid frequency of target center is compensated. The echoes model and azimuth non-uniform sampling modelforformation-flying satellites SAR is established. A novel spectral reconstructionalgorithm based on azimuth periodically non-uniform sampling is presented. We alsosolve the problems of spectrum distortion and image blurring. Based on compensatingthe error caused by different transmitting paths and reconstructing the azimuth spectral,the imaging method for formation-flying satellites SAR is proposed. We alos realize theimage withthe OCD-LFM waveforms.4. According to the data transmission characteristics of formation flight mode andmaster-slave mode of formation-flying satellites SAR, sparse matrixes, measurementmatrixes and compressive sensing matrixes of the two kinds of modes are establishedwith the properities of formation-flying satellites SAR echoes. The compressivesensing imaging methods for these two kinds of modes are proposed. The simulationresults show that the two kinds of compressive sensing methods can reconstruct theoriginal sparse target scene with less echoes data. Thus,the formation-flying satellitesSAR imaging based on low data transmission payload can be realized.