Research On Mechanisms Of Passive Intermodulation Induced By The Multicarry Multipactor And The Loose Connection

Suppressing passive intermodulation?PIM?distortion is an important precondition to ensure the safety,stability and economic operation of the mobile communication systems,it is also an important guarantee for promoting the frequency bands compatibility,co-construction and sharing of telecom infrastructure.Nearly 50years of research results show that the PIM generation can be divided into two cases,one is the nonlinearity of contact,and the other is nonlinearity of materials.However,with the wide application of new materials and new technologies in wireless communication,there are still some mechanisms of PIM generation that are not clear.Therefore,according to the characteristics of the next generation mobile communication systems,this dissertation focuses on the PIM mechanisms of the multipactor and the loose electrical contact,and the contents include:1)the spectrum analysis of the multicarrier multipactor;2)the PIM analysis of the loose electrical contact in coaxial connectors.1.The spectrum analysis of the multicarrier multipactor.Following contents are included in this part:1)The spectrum analysis of single-carrier multipactor.First,based on the steady state of the multipactor,a steady-state analysis model of multipactor is established and simulated.Then,based on the steady-state analysis model,a mathematical expression for the current density of the single-carrier multipactor is derived.One conclusion can be drawn from the mathematical expression,which is the frequency components of the electronic noise are the odd order of carrier frequency,and the electronic noise which is generated by the single-carrier multipactor.Therefore,it is convenient for designing the filters and the noise suppression devices to eliminate the electronic noise of the single-carrier multipactor.2)The spectrum analysis of multi-carrier multipactor.First,the steady-state analysis model is used to solve the instantaneous velocity of multi-carrier multipactor;Then,the instantaneous velocity is divieded into two parts:one is the continuous time component v_osc?t?,and the other is the periodic constant component v_con?t?;Finally,the Fourier transform technique is empoyed to solve the frequency components of the multi-carrier multipactor.The analysis results show that the frequency components of the multi-carrier multipactor are the odd order of the carrier frequency.Meanwhile,the third-order harmonic,the seventh-order,the nine-order and the eleventh-order subharmonic are very close to the third-order passive intermodulation.2.The PIM analysis of the loose electrical contact in coaxial connectors.Following contents are included in this part:1)The PIM mechanism analysis of electrical parameters.First,an equivalent circuit model of tight contact is established.Then,the impedance,current and S-parameter of the loose contact connectors are analyzed and simulated.Finally,an equivalent circuit model for the loose contact connector is proposed.As stated in this circuit model:the increase of current in the nonlinear resistance makes the creased PIM distortion in loose contact connector.2)The PIM mechanism analysis of the electrothermal coupling.First,an energy conversion model between the electromagnetic domain and the therma l domain is established.Then,this model is extended to the loose contact coaxial connector and further confirmed by the Multiphysics Studio of CST software.Finally,a mathematical expression,which is shown the relationship between the PIM value and the electrothermal coupling,is proposed.3)A method for testing the PIM distortion of loose electrical contacts is proposed.In the study of PIM mechanisms of electrical parameter and telectrothermal coupling,the inherent relationship between the increase of PIM distortion and the additional impedance is proposed,namely:The increased PIM level is proportional to the additional impedance.Furthermore,a novel PIM test method for loose contact connectors is established.This method does not require special and expensive passive PIM test instrument,and only needs to measure the additional impedance by the TDR instrument.In other words,it provides new ideas and new methods for the loose contact PIM testing.