Research And Design Of Multi-purpose Intermediate Frequency Signal Preprocessor Based On FPGA

In radar and wireless communication technology,Intermediate frequency(IF)signal processing has become one of the key technologies.IF signal processing connects the radio frequency(RF)signal processing and the baseband signal processing,its processing performance directly affects the collection and analysis of the subsequent signal.It plays a crucial role in the entire signal processing.IF signal preprocessing includes the connection of analog IF signals after RF signal processing and some IF signal processing functions.The purpose of this paper is to study and design a multi-purpose IF signal preprocessor based on two different sources of radar signal and instrumentation signal.It achieves the purpose of signal spectrum shifting,data rate reduction and digital filtering without distortion of the signal based on the theory of digital down conversion and decimation filtering,which reduces the pressure on subsequent signal processing.The main work of this paper includes:(1)In a radar multi-polarization identification system,a radar IF signal preprocessor is designed based on Altera FPGA.The signal conditioning module is used to complete the conversion from analog IF to digital IF.The digital down conversion module is used to complete the spectrum shift from the IF signal to the baseband and to extract the useful signal.(2)In an instrument multi-channel IF signal processing system,an instrument IF signal preprocessor based on Xilinx FPGA is designed to realize the functions of digital down conversion and digital filtering and to solve the problem that high-frequency signals cannot be analyzed due to the conflict between resolution bandwidth,signal acquisition time and frequency resolution.(3)Taking the linear frequency modulated(LFM)signal pulse as an example,the influence of the Doppler frequency shift on the pulse compression caused by the moving target in a radar multi-polarization identification system is discussed,it is concluded that the LFM signal is insensitive to the Doppler frequency,and the main lobe peak offset of the output signal is directly proportional to the Doppler frequency.The influence of the I/Q timing problem on the pulse compression in a multi-channel IF signal processing system of an instrument is discussed,it is found that when the I/Q signal is reversed,the pulse compression process loses the main lobe,the side lobes are also severely distorted,and the pulse pressure waveform cannot be properly pressed;when the I/Q signal is misaligned,although the pulse pressure waveform can still be pressed,the side lobe is slowly lifted,the main-to-side lobe ratio and signal-to-noise ratio are greatly reduced as the number of misplaced digits increases.