Research And Implementation Of Radio Altimeter Echo Signal Simulation

In the process of radio altimeter development,production and service,special signal simulation equipment is needed to generate test excitation and conduct comprehensive tests on the functions and performance of the altimeter.Compared with the field test or real aircraft flight test,this method can not only improve the development efficiency of the new model altimeter,but also can quickly analyze the fault situation of the in-service altimeter.With the improvement of altimeter measurement accuracy and the enhancement of anti-clutter interference capability,the traditional echo simulation method based on physical delay lines can no longer adapt to the testing requirements of the new altimeter,and RF processing technology needs to be introduced to complete the increasingly complex altimeter testing work,which requires increasingly sophisticated signal simulation.Thesis researches and builds a set of altimeter echo signal simulation platform based on Zero IF architecture and digital processing technology.The platform uses high performance So C FPGA as the main control chip,uses ADRV9009 broadband RF transceiver chip to complete up/down conversion and AD/DA conversion,and through FPGA echo simulation logic design,it can generate fine height echo signal in surface reflection environment and linear height change scenario,realizing the RF echo simulation function of altimeter in FM continuous wave regime.Thesis established the model of altimeter RF echo signal through mathematical derivation;combined with the altimeter national specification,formulated the test requirements and technical specifications,proposed the overall design of the system from RF to baseband,and selected the appropriate hardware to implement the design scheme;thesis studied the JESD204 B high-speed serial interface protocol,and completed the interface design based on commercial IP.The DDS orthogonal carrier generator and Doppler modulation structure were used to simulate the echo velocity information,and the velocity simulation with 0～100m/s range and 1m/s resolution was achieved;the height simulation with maximum 3000 m range was achieved based on the address cycle control strategy and dual-port RAM storage structure;studied the fine altitude simulation method based on the fractional delay filter and used the weighted least squares FIR filter with optimized structure to achieve a height simulation resolution of 0.3 m;a waveform storage and address scanning strategy is used to achieve the simulation of statistical model ground clutter.After testing and verification,the echo signal simulation system designed in this thesis can realize the echo signal simulation function of altimeter in 4.2～4.4GHz band,and the continuous wave simulation capability is partly close to that of foreign ALT-8000 altimeter testers,which to a certain extent alleviates the contradiction between the rapid development of radio altimetry technology and the relative lag of its test excitation technology.