The Hardware Design Of Continuous Wave Radio Altimeter Test

In the field of aviation,the radio altimeter is an altimetry instrument, which has been playing an increasingly important role in automatic landing. In the production and use of the continuous wave radio, It is necessary to test its performance and indicators. This paper completes intermediate frequency module design of this test equipment, whose main function is to receive measure intermediate frequency modulated signal, outputs delay echo signal that consistent with the original baseband signal,the back to the RF board.Test performance of altimeter according to the measurement of altimeter and the simulated true altitude.This article starts from the application background and the principle of continuous wave radio altimeter, proposed digital delay method to implement design features. In this design, The main control unit is FPGA, and meet to comparator, AD, DDS and other chip to receive, measure of signal and generate analog echo signal. FPGA is mainly used to measure the signal and generate echo signal, and DDS is used to generate analog signal from 50 MHz to 250 MHz.This article also elaborates how to achieve logic function in FPGA on intermediate frequency circuit board. The middle frequency board will receive middle frequency signal and envelope signal from RF board and parameters from PC, then the frequency measurement unit will measure the frequency of signal and fit the slope, generating the echo frequency value according to the slope. Delay and counting module begin to work when frequency measurement value within the set rang. the FPGA will output the value of frequency saved in RAM to DDS when time is up, and DDS will generate the corresponding analog signal. At the same time, It is need to measure the RF parameters of the baseband signal to characterize the property of the altimeter of the transmitted signal...