Research And Implementation Of Signal Processing Method Of FMCW Radar Altimeter

Radar altimeters are indispensable airborne electronic devices in many aircraft.They can accurately measure the altitude of aircraft carriers and the ground.They have been widely used in various military and civilian equipment.Frequency Modulation Continuous Wave Radar altimeters of constant beat-frequency has a series of advantages such as strong anti-interference,no distance blind zone,low transmission power,light weight and small volume.As the demand for users is getting higher and higher,and the application scene of radar altimeters is becoming more and more complex,people have also put forward higher requirements on the performance of radar altimeters.The purpose of this paper is to design and implement a radar altimeter digital signal processing system,which has strong resistance to disturbances,has strong adaptability to terrain,climate,and so on,and has a high measurable range,high real-time processing and high stability.In this paper,based on the FMCW technology,a constant beat frequency system is used.Before extracting the front of the frequency spectrum of the surface target beat signal,a band-pass filter with a narrow bandwidth is designed to filter the beat signal so that most of the interference in the surface target beat signal can be filtered out.So the anti-interference performance of the system is greatly enhanced.In order to meet the requirements of the system's adaptability to the environment such as landscape,climate and altitude,the power control module and the beat signal amplitude control module are designed.The system can control the transmit power and the beat signal amplitude gain according to the received power and the amplitude of the beat signal.In this way,the system can emit less power in a highly reflective environment and emit more power in a less reflective environment.This ensures that the receiving power of the system in different reflective environments is not too small or too large to affect its normal operation.At the same time,it also reduces the probability of the system being intercepted.The system adopts different processing methods for different altitudes.The entire measurement height is divided into four intervals.The parameters of each altitude interval algorithm are designed,which not only can ensure the high height measurement range of the system,but also can improve the working efficiency of the system.In addition,the system designs some relatively robust algorithms to ensure the stability and reliability of the system measurement results,such as height search and altitude tracking.Finally,based on the consideration of system real-time and complex algorithms,this system is based on FPGA + DSP architecture to design and implement FIR,FFT and other related digital signal processing,and finally complete system functions.