Design And Implementation Of X Band Frequency Modulated Continuous Wave Radar Transceiver Front-end

Compared with pulse radar,frequency modulated continuous wave radar has the advantages of no measurement blind area,low power consumption,high linearity and high resolution.It has been widely used in vehicle collision avoidance,life detection,accurate ranging and other fields.The transceiver front end is an important component in frequency modulated continuous wave radar system.It is mainly responsible for RF signal transmitting and receiving,and its performance directly affects the working index of radar.Therefore,the transceiver front end of frequency modulated continuous wave radar has important research significance.This paper designs and implements an X-band frequency modulated continuous wave radar transceiver front end.The transceiver front-end is divided into three parts:frequency source,transmitter and receiver.The transmitter and receiver are installed in the same cavity module,and the frequency source is a single module cavity,which can be disassembled or connected between modules.The overall size is 10cm×10cm×2cm.DDS scheme is adopted as the frequency source.Crystal oscillator is used to generate a low frequency reference signal of 100 MHz,and then the frequency is multiplied to 2.4GHz by a 24 frequency multipling link.The 2.4GHz signal is used as the reference clock of DDS chip AD9914,and the register value of AD9914 is assigned by FPGA control system.Finally,900±25MHz sweep signal is generated.The sweep step of the frequency source is 1KHz,the period is 2ms,the output signal power is-11.7d Bm,and the phase noise is-123 d Bc/Hz@1KHz.The transmitter uses frequency multipling link to perform 10 frequency multipling of DDS sweep signal.In order to enhance the frequency selection characteristics of the transmitter,a microstrip filter with a passband of 8.6-9.44 GHz is designed,and a power amplifier is used to amplify the signal to sufficient power at the last stage.The measured frequency sweep range of the transmitter is 9000±250MHz,the transmitting power is29 d Bm,the flatness is 2.4d B,the output phase noise is-103 d Bc/Hz@1KHz,and the stray suppression is 26.6d Bc.The receiver adopts direct down conversion scheme,the circuit is composed of IQ mixer and IF amplifier,in which the local oscillator signal of IQ mixer is coupled from the transmitter end.IF amplifier is realized by operational amplifier + passive filter.Finally,the working frequency band of the receiver is 9000±250MHz,the gain is 61.5d B,and the noise coefficient is less than 6d B.After the three parts work normally,comprehensive test of transceiver is carried out.A 20-meter coaxial cable is used to connect the transmitting and receiving ends to simulate echo signal,and a 50 d B attenuator is used to simulate space loss.Finally,the line length is calculated as 22.12 m from the difference frequency signal waveform,which is basically consistent with the actual line length.The focus of this paper is to control the phase noise of transmitter to improve the accuracy of radar work,so the frequency source structure of DDS scheme is adopted.In addition,the frequency multipling transmitter and direct down conversion receiver are designed with the central idea of miniaturization.In conclusion,this paper provides a feasible scheme for the front-end design of X-band FMCW radar.