Passive Intermodulation For Contact Nonlinear On Microwave Device

Passive intermodulation(PIM)is a nonlinearity phenomenon when two or more signals are through a passive nonlinear component,such as microwave coaxial,load and antenna.This process will generate other signals because of the nonlinearity.And the new generation signals generated from this nonlinear phenomenon are called passive intermodulation products(PIMP).When the PIMP received by the antenna,it will lead that the spectrum resource tensed,the communication channel blocked and the communication quality reduced.With the development of antennas on high power and high sensitivity,the power level of PIM will increases with the greater of input power.When its power exceeds the system noise threshold,it will further affect the normal operation of the system,and the communication system will be paralyzed seriously.Therefore,the in-depth study of PIM is very urgent.At present,in order to solve the problems of PIM nonlinearity in complicated mechanism and difficult prediction,the article is divided into the following parts to research:1.The method of PIM nonlinear analysis and modeling for single point source contact of microwave connector was developed.The nonlinear mechanism analysis of point contact is closely related to the microscopic contact of metal,the roughness of the material surface,the contact pressure and the surface temperature.Based on the Weierstrass-Mandelbrot(WM)model,the actual three-dimensional rough contact surface is expressed through fractal dimension and fractal roughness.Aiming at the problem that it is difficult to identify the fractal parameters of real contact rough surfaces,a method of power spectral density is studied,which can extract the fractal surface parameters guaranteeing accuracy.Based on the physical effects of metal-metal micro-contact,a metal-metal micro-contact equivalent circuit model is established,and the I-V characteristic of point source of nonlinear contact is obtained.Based on Newton's binomial theorem,a nonlinear calculation formula for single point source is established.2.The method of PIM power level prediction for microwave connector cascade system was developed.A large number of microwave devices are cascaded in the measurement and control antenna,and there are few studies on the cascaded microwave devices.In order to solve the problem that the PIM power level is difficult to predict in the cascade system,the relationship between the single microwave connector PIM and the cascade system PIM is studied in this paper.Based on the transmission line theory,a mathematical model of the total intermodulation voltage of the signal receiving terminal and the intermodulation voltage of the single point nonlinear source is derived when multiple microwave connectors are cascaded.Finally,a method for fast prediction of cascaded system PIM is established.3.The method of PIM experimental verification of the nonlinear model for microwave connector was developed.Using the DIN(7/16)coaxial connector as the test object,the fractal parameters of different contact rough surfaces are identified.Third-order PIM power level of the connector is calculated under different input power,different preload,different number of cascades and vibration conditions.PIM test is carried out under the same conditions,and the theoretical calculation is compared with the experimental value.The variation of the PIM power level in the microwave connector under different input conditions is revealed,and the accuracy of the method and model proposed in this paper is verified.