The Millimeter-Wave Front End With Its Applications In Imaging System

Millimeter-wave radar imaging system has great potential in security inspection,non-destructive testing and other fields.As an important hardware part of radar imaging sys-tem,RF front end needs to determine its performance index and structure according to the requirements of the system.What is the connection between the radar imaging system and its RF front-end subsystem? How to design the RF front end of radar imaging systems?To solve the above problems,this paper mainly carried out the following research:1.In imaging system design process,the performance indexes of RF front-end trans-mitter,receiver and frequency synthesizer are largely determined by the algorithm and system.In this paper,some relationship of RF front end and radar imaging system is ana-lyzed,so as to better select the structure of the hardware.For the transmitter,the operating frequency is usually determined by the choosen imaging resolution and the state-of-art hardware conditions.The LF modulation reduces the transmitting power and dechirping well by heterodyne receiver.For the receiver,the imaging reconstruction algorithm re-quires a dynamic range of more than 30 dB,which can be estimated by calculating the RF front-end cascade noise.The equilibrium of orthogonal I/Q mixing needs to make its mir-ror rejection ratio greater than 30 dB.And the frequency synthesizer should be designed on the premise of ensuring the coherence of the system.2.The circuit principle of balanced multiplier and subharmonic mixer based on anti-parallel diode pair(APDP)is analyzed.On the basis of balanced tripler and subharmonic mixer,the following two key modules are developed:(1)A six times frequency multiplier module whose input is 15.4-17GHz and output is 92.4-102GHz.The broadband output power of 8dBm input is higher than 3dBm.(2)A subharmonic mixing module,which con-tains up-conversion of local oscillator.When the fixed intermediate frequency is 4.8GHz,the total conversion loss is about -15db.3.A W-band RF front-end subsystem is designed by using the six times frequency multiplier module and subharmonic mixing module.It mainly includes frequency synthe-sizer module,transmitting up-conversion module,the first local oscillator up-conversion module and orthogonal IF module.The coherent system which use multi-frequency source is realized,and the I/Q signal of zero IF is obtained in the orthogonal IF module.The transmitter and the reciever are connected for testing.The RF front end performance index basically meets the requirement.Finally,an image of the experimental results is presented.