Research On Hybrid Baseline Multi-Channel High-Resolution And Wide-Swath SAR Imaging

As an active detection system,Synthetic Aperture Radar(SAR)has the characteristics and advantages of all-day and all-weather operation.It has been widely used in land surveying and mapping,resource exploration,marine monitoring,military reconnaissance,intelligence collection,battlefield surveillance and other fields.The application of multi-channel SAR and digital beamforming technology overcomes the problem of minimum antenna area limitation in single-channel SAR,and realizes highresolution and wide-swath SAR imaging.Due to the existence of both along track and cross track baselines between the receiving channels,the hybrid baseline multi-channel SAR system has the potential and advantages of high-resolution and wide-swath imaging,interferometry,receiver anti-interference,low-cost miniaturization and other applications.In this paper,high-resolution and wide-swath SAR imaging is taken as the research target,and based on multi-channel azimuth signal reconstruction,a series of problems caused by the introduction of hybrid baselines between channels are analyzed and processed.The main work of this paper is as follows:1.For the hybrid baseline multi-channel system,based on the equivalent phase center theory,the quadratic model of the slant range equivalent error is derived and established.According to the spatial geometric model,the slant range from the target to each receiving channel is affected by both along-track baseline and vertical-track baseline.Compared with the existing multi-channel high-resolution and wide-swath algorithm,the slant range equivalent error is regarded as a constant or a linear model is used.When the vertical heading baseline is large,the processing performance of the azimuth signal reconstruction algorithm of the slant range equivalent error quadratic model established in this paper is significantly improved.In this paper,the quadratic model of equivalent error of slant range is established,which fully considers the influence of cross track baseline and swath.The model can lead to a phase error of less than 2 ° with swath of 100 km and a cross track baseline length of 3 km.Finally,the influence of azimuth time,swath and terrain on the equivalent error of slant range is analyzed,and it is pointed out that it has time-varying and space-varying characteristics,which lays a foundation for subsequent high-resolution and wide-swath imaging.2.The key parameters of the hybrid baseline multi-channel SAR system are designed,including wave position,pulse repetition frequency,antenna length,transmitting signal bandwidth and the number of receiving channels.The ambiguity and sensitivity of the system are verified by using range-ambiguity-to-signal ratio(RASR)and azimuthambiguity-to-signal ratio(AASR)and noise equivalent sigma zero(NESZ).It is verified that the RASR of each wave position is lower than-30 dB,the AASR after ambiguity suppression is lower than-20 dB,and the NESZ of each wave position is lower than-20 dB,which meets the design requirements.At the same time,based on the traditional azimuth multi-channel high-resolution wide-swath imaging algorithm,a hybrid baseline multi-channel high-resolution wide-swath SAR imaging algorithm is designed.The algorithm solves the problem of range mismatch introduced by hybrid baseline through range envelope registration and phase compensation,and then realizes high-resolution wide-swath SAR imaging after multi-channel azimuth signal reconstruction.The simulation results show that the AASR of the target located in the center of the scene is less than-19 dB,where the swath is 50 km and the resolution is 3 m.