The Research Of Digital Cancellation Technology In A SFCW Radar System

Compared with the pulse radar,the frequency modulated continuous wave(FMCW)radar has advantages of higher range resolution,smaller size,larger time-bandwidth,no distance blind area,simple structure,light weight,low cost and so on.So FMCW radars have widespread applications in Automotive Anti-collision Radars,traffic monitor system,microwave exploration or other aspects.But the leakage of the FMCW radars decrease the operating distance of the radars.This shortage limits the development of FMCW radars.The leakage of the FMCW radars is reduced to a low level by using the method of RF cancellation circuit of digital controls.The main work of this paper is to design a stepping frequency radar,including phaselocked source,the transmission link,the reception link,the data acquisition part,and then apply the RF cancellation technology to the stepping frequency radar.Firstly,this paper introduces the background,the domestic and international situation of the research,the research significance of the subject.Then analyzes the existing problems in the FMCW radars.In this paper,I summarized and contrasted the methods used to decrease the leakage signal.It emphasizes on the principle of RF cancellation technology and implementation methods used in this system.On this basis,I designed the RF cancellation circuit of digital controls.The RF cancellation process is divided into three processes: sampling,calculation and control.The amplitude and phase of the leakage signal was detected by sampling,and then it provides the I/Q inputs to the vector modulator that controls the amplitude and phase of the feed-through signal.If the feed-through signal is made to be of equal amplitude and contrary phase to the original leakage signal,the summation of two will cancel each other,the cancellation is realized on the reception link.After the debugging and analyzing of the hardware system,the cancellation of the experiment was completed,this method offers precise control of the RF cancellation module.The experimental results were: the cancel ratio can get 30 dB from 1.8GHz to 2.0GHz.Finally,it summarizes the achievements,conclusions and the existing problems of the paper.