| Circular trace scanning synthetic aperture radar,which can work both in continuous wave system and pulse wave system containing 14 working modes,has the characteristics of all day long and all-weather and also can meet various range and multiple range and azimuth resolution requirements.The circular trace scanning SAR consists of the upper computer,the analog front-end system and the digital signal processing system.Compared with the traditional SAR imaging,with 360 degree vision,it has a wide range of imaging effect of high scanning speed and the advantage of achieving a wide range of imaging results in a short time.Digital signal processing and imaging algorithms of Circular trace scanning SAR are implemented by FPGA+DSP architecture,which take into account the advantages of two kinds of digital devices and greatly improve the speed and flexibility of digital processing of echo signals as well as the efficiency of the algorithm to meet the needs of real-time imaging of the system.In this paper,some theoretical research,system implementation and overall debugging of the ring scan SAR system based on FPGA+DSP are made.In this paper,the basic principle of ring scan SAR imaging is analyzed,and the signal model and high resolution imaging algorithm suitable for this system are studied.The SAR range and azimuth spectrum of ring sweep is given,and under certain conditions,the azimuth direction of the ring scan SAR echo can be treated by linear frequency modulation.Secondly,the design scheme of the circular trace scanning SAR system is given,and the composition,working principle and function of the analog front end system are described in detail.The waveform control,the data path,the sampling and the digital signal processing mode of the signal processing system which are compatible with the two kinds of waveform systems are discussed.Then 14 working modes of the waveform control pulse are designed with FPGA.With different data transmission requirements,the configurations and uses of analog to digital converters(AD)and three communication interfaces,which are SPI,UART and Rapid IO.The process of FPGA imaging preprocessing and two-dimensional high resolution imaging with DSP is also studied.At the end of this paper,the circular trace scanning SAR system has been fully tested.According to the 14 working modes of the two wave forms,the performance of waveform control,data transmission and imaging preprocessing in the signal processing system is tested and analyzed,and the test results with continuous wave system working mode 1 as an example are given.Then the performance of the analog front-end system were analyzed in detail,aquiring the in-band and the out-off-band spetrums of the microwave,transmitter and receiver,and verify the input and output range of the receiver.The isolation of the analog front-end system is presented.After the performance test of each subsystem was completed,the closed loop test of the circular trace scanning S AR was carried out,and the open loop test was carried out in the darkroom after the effective results were obtained,and it is compared with the simulation result of the high-resolution imaging and the antenna phase influence of the circular trace scanning SAR.At last,the problems and solutions in the process of testing and testing are described in detail,and the suggestions for the use of the SAR system are given according to the existing test conditions. |
