Ka-band Broadband FMCW Radar System Design And Implementation

At present,with the rapid development of microwave technology,the frequency and bandwidth of radars have been continuously improved,and the application fields have become increasingly widespread.Millimeter-wave Frequency Modulated Continuous Wave(FMCW)radar has the advantages of high integration,low cost,large instantaneous bandwidth with low sampling rate,etc.It can carry out uav monitoring and identification,airport runway debris detection,non-contact security and other tasks well,which makes the millimeter-wave FMCW radar become the current research hotspot.This paper proposes a design method of Ka-band full-coherence FMCW radar system for high-resolution imaging of small targets,solves the common problem of periodic frequency-modulation nonlinearity in FMCW radar systems,builds a radar RF front-end based on Monolithic Microwave Integrated Circuit and solid-state devices and FPGA-based data processing system,and develops FMCW radar imaging software.The main work and results of the thesis are as follows:1.The principle of sawtooth FM ranging of FMCW radar is studied in depth.According to the actual application requirements,system indicators are selected.For the system's requirements for miniaturization,this paper adopts a simple structure of the signal generation and zero-IF reception mode.In view of the precision of system timing operation,the overall layout of FPGA is adopted in software design.Because the radar signal phase correlation processing can obtain higher accumulation effect and improve the ability to detect weak targets,this paper focuses on the analysis and design of digital phase coherent and the analog phase coherent.2.The Ka-band FMCW radar system is divided into several sub-modules,and detailed scheme design and implementation are carried out.Firstly,in order to achive high-performance Ka-band broadband,this paper adopts X-band Phase-Locked Loop(PLL)generation,4 frequency multiplier and proper frequency filters.Then,for the echo receiving circuit,a zero-IF receiving structure with lower system sampling rate is designed,and a frequency gain conditioning circuit is introduced to solve the problem that radar long-distance echo is easily submerged by noise.In order to guarantee the signal acquisition accuracy and transmission quality,detailed analysis and design of the controllable gain amplifier(VGA),A/D acquisition,FPGA signal processing and network port transmission circuit are realized.According to the system's overall requirements for coherence,a stable and easy-to-synchronize clock circuit is adopted.At the same time,the power supply circuit of the system is optimized to reduce the mutual interference of digital and analog power supply.Finally,The hardware system test results show that the system can achieve signal phase noise less than-84.79 d Bc/Hz@10kHz in the Ka band 34.4-39.2GHz sweep range,and the spur is better than the 52 d Bc;the receiver circuit can achieve high-quality amplification,acquisition and transmission of weak IF signals with a frequency of 80 kHz and a power of about-90 dBm.3.Aiming at the problem of range image degradation due to periodic nonlinear frequency modulation in radar echo,the cause reasons space-change characteristics of the paired echoes are analyzed and a multi-component sinusoidal frequency modulation parameters estimation algorithm based on the combination of matching initial value and nonlinear least squares are proposed.The method of estimation and the use of matched Fourier transform(MFT)for nonlinear correction of the signal significantly improve the quality of the distance compression.On the basis of good radar pulse coherence,high-resolution Synthetic Aperture Radar(SAR)imaging of corner reflectors,copper cylinders,and aircraft carrier models is performed using ?k imaging algorithms.The range resolution is better than 4.24 cm,azimuth resolution is better than 0.95 cm,which preliminary achieves the final goal for high resolution imaging of small target.