Design Of High Speed Data Acquisition And Transmission For Synthetic Aperture Microwave Radiometer

Under the background of global climate change,extreme weather events such as typhoons occur frequently.In order to reduce the heavy losses caused by typhoons,it is necessary to describe more accurately the spatial and temporal distribution characteristics and variation rules of global climate brightness and temperature,which requires high spatial resolution of radiometers.The traditional real-aperture microwave radiometer is limited by the physical size of antenna and its spatial resolution is very limited.The application of"synthetic aperture"technology can effectively alleviate this bottleneck.However,the application of integrated aperture technology also has some costs.In order to construct a high spatial resolution synthetic aperture radiometer system,a large number of antenna receiving units need to be placed in the antenna array,which will make the radiometer face high hardware costs and manufacturing difficulties;moreover,in the future potential applications,higher spatial resolution is needed,the number of antennas in the array will increase correspondingly,and the scale of signal acquisition channels will rise rapidly to tens.It's hundreds of roads.Using so many receiving channels will face great challenges.The large system scale and high system complexity of synthetic aperture radiometer make it difficult to implement data acquisition system in an integrated way.Therefore,the system can only be built in a distributed structure.At the same time,it requires the digital system to achieve synchronous acquisition and high-speed data transmission between boards.Based on the above situation,a high-speed data acquisition and transmission system with 24 channels and 60 Msps sampling rate is proposed and designed for the huge system scale and digital system in space exploration mission.The digital system is mainly designed around AD acquisition board,CNC board and back-end related board.The specific content mainly includes the following points:(1)On the hardware side,the traditional cables are abandoned between the sub-boards and the related boards and the optical fibers are used to realize data transmission.The physical layer is the Racket I/O GTX transceiver built in the Virtex-5 series of FPGAs provided by Xilinx,which realizes the high-speed optical fibre link between the majority of digital sampling arrays and the large-scale digital correlation back-end units.In order to realize the synchronous data acquisition,this paper takes the 60MHz sampling clock as the physical layer.For example,based on the idea of multi-level distribution,a high-performance synchronous clock distribution link is designed,the chip selection is completed,and the control logic design of synchronous data acquisition is realized.(2)In order to realize the serial transmission of high-speed data in the programming of FPGA,this paper takes the GTX high-speed transceiver built in XC5VFX130T as the physical layer to complete the functions of parallel-to-serial conversion,encapsulation,parsing,transmission and reception of data,and realizes the logical design of data transmission based on the Aurora protocol;aiming at the clock synchronization scheme proposed in this paper,multi-channel data synchronization is completed in the ISE environment.The control logic is collected and the synchronization performance is analyzed.(3)The experimental analysis is carried out.Firstly,the synchronous data acquisition of different channels is tested on the board.The waveforms are observed by chipscope and the acquisition sequence of each channel is fitted in MATLAB to obtain the phase information of waveforms of each channel.By analyzing the results of many measurements,it can be concluded that the phase delay between different channels is less than 1.5 degrees and the phase jitter is about 0.1 degrees,which meets the requirement of phase synchronization in AD acquisition.The data transmission function is validated and the BER of the system is less than 10~-77 that of the distributed system.In conclusion,the system meets the needs of data acquisition and transmission,and is suitable for the design of digital system of large-scale integrated aperture microwave radiometer.