Design Of Fast Frequency Measurement Module In Radar Target Simulator

As a typical radar test instrument,radar target simulator plays an important role in verifying radar target resolution,multi-target real-time processing and so on.With the development of electronic technology,the radar target signal has been developed from a fixed carrier frequency pulse signal to a variety of standard signals with characteristics of wide band and frequency agility,the frequency measurement module is used to measure the carrier frequency of the radar quickly and accurately,and the Frequency Agile unit is configured according to the frequency measurement information to make its output frequency correspond to the working frequency of the radar,so as to realize the function of fast target locking and tracking.At present,the common carrier Frequency Tester only accomplishes the fast measurement of the frequency of the radar carrier signal,while the measured frequency value does not directly affect the other modules of the target simulator.In this paper,based on the fast and high-precision measurement of carrier frequency of radar target analog signal,the fast frequency synthesis unit is added to realize the full-function coverage of ‘frequency measurement + frequency calculation + frequency synthesis'.At the same time,the frequency synthesis unit output signal is used as the reference signal of the secondary down-conversion,and the baseband signal is obtained by mixing with the Intermediate Frequency Signal,which reduces the performance requirement of the secondary Analog-to-digital converter.The main research contents of this thesis include:Reserach the carrier frequency measurement methods for different carrier frequency(continuous wave,pulse wave,etc.),and several main methods of frequency synthesis,including direct digital frequency synthesis(DDS),the frequency multiplier link and PLL frequency synthesis(PLL)are analyzed,and the frequency measurement module is designed according to the practical requirements of frequency agility.Design the hardware implementation scheme based on TDC + FPGA + DDS.The detailed hardware design schemes of RF signal gain automatic control unit,multi-stage frequency divider unit,TDC measuring unit,DDS + PLL frequency agile and so on,and the corresponding power conversion circuit is designed.Analyze the influence of harmonics and spurious of output signal of DDS and PLL.By using Genesys simulation software the frequency synthesis scheme is given.At the same time,study the realization of receiving and processing frequency measurement data and synthesizing frequency control logic in FPGA based on Ise14.7 platform.According to the design scheme,the hardware of the frequency measuring module is made and debugged,and the actual function of the hardware circuit is tested by using oscilloscope,spectrum analyzer,signal generator,etc.,it is verified that the key parameters such as frequency measurement accuracy and frequency conversion time meet the design requirements.The test results show that the input signal with a dynamic range of 40 dB at 100MHz-2GHz can be quickly measured with an error less than 1MHz,and the frequency agility function within 1.2?s can be realized.This design lays a solid foundation for the following development of wideband radar target simulator.