Research On The Modeling Of Passive Intermodulation Interference In Coaxial Connectors

Passive intermodulation(PIM)refers to the generation of signals with different frequencies from the carriers in the output signal when two or more frequencies are input into a passive nonlinear device.These new frequency signals may fall into the receiving frequency bands and cause interference.With the widespread application of high-power transmitters and transceiver multiplex antennas,the high demand of receiver sensitivity,and the increasingly dense communication frequency band,PIM interference has gradually become prominent,and it has become an important factor affecting the signal transmission quality of communication system.Coaxial connector is a basic passive component which is most used,most varied and prone to failure in the whole radio frequency communication system.It plays the role of signal transmission between modules,and it is considered to be the main nonlinear source of PIM interference in the communication system.In addition,coaxial connectors are often used in harsh environments,the comprehensive effect of environmental factors will lead to the degradation of connectors and the deterioration of their PIM performance.Therefore,the research on PIM in coaxial connectors is of great significance to reduce PIM interference and improve the reliability of communication system.In this thesis,the research on the modeling of passive intermodulation interference in coaxial connectors includes four parts.They are respectively the study on generation mechanism and modeling of PIM in coaxial connectors,the impact of multiple insertions and withdrawals,and vibration on PIM performance in coaxial connectors,the impact of corrosive environment and temperature cycle conditions on PIM performance in coaxial connectors,and the study on PIM performance in coaxial connectors excited by different types of input signals.These four parts are interrelated and complementary.The research methods include theoretical derivation,simulation analysis and experimental verification.The nonlinear characteristics and PIM performance of coaxial connectors are studied comprehensively and thoroughly from micro analysis to macro modeling.The research results of this thesis are helpful to analyze the PIM performance in coaxial connectors under different environmental conditions and the PIM performance in coaxial connectors excited by different types of input signals.At the same time,the research results of this thesis have significant value for the design of coaxial connectors used in special environments.In addition,the research methods in this thesis can be extended to other passive devices and systems.The main contributions of this dissertation are concluded as follows.(1)Using a polynomial model as the behavior model describing the nonlinearity of coaxial connectors,the formula of any order two-tone PIM product power is derived.Based on the tunneling effect,a novel polynomial mathematical model is established to describe the nonlinear characteristics of coaxial connectors.A mathematical model based on sine function is proposed to describe the nonlinear characteristics and PIM performance of coaxial connectors.Taking error vector magnitude as an index,the signal distortion of communication system is analyzed and calculated when the distortion caused by the nonlinearity of coaxial connectors,phase noise,and additive Gaussian white noise exist simultaneously.(2)A series of multiple insertion and withdrawal experiments,radial vibration experiments,and axial vibration experiments are designed and performed in order to produce coaxial connectors with different degradation levels.The mechanism of the impact of multiple insertions and withdrawals,and vibration environment on PIM performance in coaxial connectors is analyzed using the electrical contact theory and the tunneling effect.Taking insertion force as the index to measure the degradation level of the coaxial connectors,a PIM prediction model of coaxial connectors with different degradation levels caused by multiple insertions and withdrawals,and vibration environment is established based on the tunneling effect.The correctness of this model is verified by a series of two-tone PIM tests.(3)A series of accelerated degradation tests with corrosive gas as environmental stress are designed and carried out in order to produce coaxial connectors with different degradation levels.Taking contact resistance as the index to measure the degradation level of the coaxial connectors,a PIM prediction model of coaxial connectors with different corrosion degradation levels is established.The correctness of this model is verified by a series of two-tone PIM tests.The impact of temperature cycle environment on PIM performance in coaxial connectors is analyzed by multi-physical field finite element simulation.A series of PIM real-time tests of coaxial connectors in temperature cycle environment are carried out.The reason for the changes of PIM performance in coaxial connectors during the temperature cycle accelerated degradation test is explained using the results of finite element simulation.(4)Based on the skin effect,the impact of signal frequency on the current density distribution in coaxial connectors is analyzed.Based on the magnetoresistance effect,the impact of signal frequency on the equivalent resistance of magnetic material region in coaxial connectors is analyzed.Considering the above two factors,the impact of signal frequency on PIM performance in coaxial connectors is analyzed.A PIM prediction model of coaxial connectors with different input signal frequencies is established.The correctness of this model is verified by a series of multiband PIM tests.The equivalent mathematical model of broadband signal and the PIM prediction model of coaxial connectors with broadband signal excitation are proposed.A series of broadband PIM tests are performed in order to verify the proposed models.