Research On RF Front-end Design Of Passive Intermodulation Test Machine

Today,with the rapid development of information and communication technology,high-power and large-scale communication has become the normal in the industry.In this context,the Passive Intermodulation(PIM)phenomenon becomes more and more important because of the nonlinearity of some system components.However,if the passive intermodulation products generated by the phenomenon of passive intermodulation enter the frequency band of the system receiver without control processing,the performance of the receiver will be greatly reduced,and in serious cases,fatal damage may be caused to the system.So the test of passive intermodulation and the research of intermodulation source location technology have become the important content of relevant industry researchers at home and abroad.Starting from the historical background of passive intermodulation,this paper first analyzes the significance of passive intermodulation and the research on testing and positioning technologies.It also introduces the current situation of passive intermodulation theoretical research and test technology research by scientists at home and abroad.Secondly,this paper analyzes the physical mechanism of passive intermodulation,describes passive cross-modulation from the perspective of data model,and analyzes some problems and challenges faced by passive cross-modulation test.Finally,this paper presents a test scheme for passive intermodulation distortion and two algorithms for locating passive intermodulation distortion sources.The positioning algorithms are as follows: k space inverse Fourier Transform algorithm based on intermodulation reference signal and PIM location algorithm based on frequency modulated continuous wave.The former uses the switching control loop to form two receiving states by setting the intermodulation reference circuit,and constructs the received vector information into the k-space function.The Position information in the L-domain is obtained through the inverse Fourier transform of the k-space function,and then the location of the intermodulation distortion source is realized;The latter is to solve the propagation delay between the PIM distortion source and the measurement end of the intermodulation signal from different angles of propagation delay in different circuits of the system,and then to locate the intermodulation fault source.Based on the proposed test scheme,this paper completes the RF front-end circuitdesign of passive intermodulation test machine,and carries out simulation verification on Matlab/Simulink platform for PIM positioning algorithm based on frequency modulated continuous wave.As for the Design of RF front circuit of passive intermodulation test machine,this paper is mainly divided into three modules: crossover generation module,crossover reference module,and receiver processing module.The cross modulation generation module is the key point of the scheme implementation in this paper.The PIM generation module HMC835LP6 GE fractional N frequency PLL chip to provide two excitation source.The inter-modulation reference module adopts the passive intermodulation generator circuit structure provided by agilent.The system processing module also provides two signals through the HMC835LP6 GE chip,which realizes the down-conversion processing and subsequent algorithm processing of the received passive passive intermodulation signal.The entire system is controlled by the zynq-7000 chip.Finally,the experimental test of the designed circuit is carried out,and the results show that the design of this paper can basically meet the requirements of the project.