Junyu Luo

To elucidate the mechanism behind the passive intermodulation (PIM) power jump phenomenon observed during dual-tone intermodulation (IM) testing, the work investigated the nonlinear transient behavior of contact interfaces induced by relative micro-movements. The concept of PIM power jump was formally introduced, accompanied by a time-domain transient analysis. A second-order parallel RLC circuit was used to fit the waveform of PIM power jumps. A time-domain model for PIM power jumps was theoretically developed by coupling mechanical dynamics, microscopic surface mechanics, and electrical contact theories. To support this model, an equivalent spring-mass system model of the contact interface, a statistical finite element model of micro-asperities, and an equivalent contact impedance model were established to predict the PIM power jumps. In addition, a series of PIM power jump observation experiments under different mechanical shocks was conducted with connectors of varying tightness. The predicted responses show strong agreement with experimental measurements, validating the accuracy and applicability of the proposed model. This analytical approach provides a solid theoretical foundation for mitigating detrimental PIM power jump effects in radio frequency (RF) systems.

This paper analyzes the phenomenon of third-order intermodulation (IM3) power jumps during temperature cycling, and proposes a prediction method for estimating the probability of IM3 power jumps in coaxial connectors. Preliminary real-time measurement has shown that the passive intermodulation (PIM) products of coaxial connectors can be divided into two parts: steady-state and dynamic-changes during alternating high and low temperatures. Therefore, separate studies are conducted on these two parts and predictive models are established. First, a nonlinear expression for calculating the current density of coaxial connectors under varying temperature was derived based on the thermionic emission effect. The stress-strain relationship during temperature cycling at the contact surface was studied through finite element analysis (FEA) simulations. Combining the thermionic emission current and electrical contact theory, a steady-state PIM prediction model for coaxial connectors was established. Then, the influence mechanism of temperature cycling on the PIM power jumps in coaxial connectors was elucidated. According to the experimental results and predicted data of the steady-state PIM, the jump index was introduced, and the grey system method (GM) was used to predict the probability of the PIM power jumps. Finally, a series of temperature cycling tests were conducted to monitor the power of PIM products in real-time, verifying the accuracy of the proposed method. Furthermore, the Poisson method is applied to evaluate the effects of temperature ranges, temperature change rates, and contact areas on the probability of PIM power jumps. The proposed method addresses existing limitations in understanding PIM power jumps and offers a novel approach to detecting performance failures in coaxial connectors, thereby providing valuable guidance for improving the reliability.

In this letter, a novel broadband passive intermodulation (PIM) model was developed to evaluate the spectral regrowth around PIM signals. This proposed model adopts the frequency division method to divide the PIM products and introduces the modified Gaussian distribution to fit the probability density function (pdf) of the PIM spectrum. Compared with the power division model, the proposed frequency division model can achieve accurate spectral regrowth estimation in a selected channel. Finally, an example of a coaxial connector was selected and a series of broadband PIM tests were conducted to verify the effectiveness of the model.

This work first reports a radio frequency (RF) tee coaxial connector, which is three-port reciprocal as a linear system but nonreciprocal as a nonlinear system. Initial experimental observations show that when the bend path of a tee connector is involved, stronger nonlinearity is found, manifested in the higher amplitude third-order intermodulation (IM3) products. According to the experimental result, the bend nonlinearity is introduced to provide explanations for extra passive intermodulation (PIM) generation in the bend of connectors resulting from nonlinear resistance and inductance caused by concentrated current density in the bend. A comprehensive analysis for bend nonlinearity was carried out using an equivalent circuit model and a finite element analysis (FEA) model, along with experimental verification. Accounting for the reflections and the extra PIM sources in the bend, an equivalent circuit model of bent connectors was developed. Considering the concentrated current density in the bend, the modified mechanism of nonlinear resistance and inductance with three modifications was investigated and an FEA model of bend was developed to evaluate the bend nonlinearity. Varying geometric parameters of the coaxial connector bend structure were simulated. It was shown that this model can be used to theoretically predict the PIM product levels for a wide variety of bent coaxial connectors. In addition, a series of PIM tests were conducted with two groups of customized bent coaxial connectors with different curvature radius, radius, and angle of bend. The measured results agree well with the predicted results, verifying the proposed model of bend nonlinearity.

A novel method for modelling the passive intermodulation (PIM) in radio frequency (RF) devices, which works as a complex non‐linear system, was proposed. Both behaviour modelling and experimental validation were introduced to clarify the generation of PIM in a parallel and series non‐linear system. Taking the coaxial connector as an example, two types of N‐type connectors with 4 and 6 contact petals were selected and put into research. The measurements both agree well with the predicted results, validating the proposed model.

Fuzz buttons connectors are widely used in printed circuit board (PCB) vertical interconnection. They provide both mechanical support and electrical connection for the circuits. In order to reduce electromagnetic wave reflection at fuzz button connector transitions resulting from impedance discontinuity, suitable physical dimensions and dielectric material in interconnections area are needed. In this work, a Finite Integration Time Domain (FITD) model for the research objective composed of waveguide PCBs and fuzz-button connectors was developed, and its corresponding SPICE model and Finite Element Analysis (FEA) model were also presented. The FITD model results were consistent with the SPICE and FEA model results. Using the obtained FITD model, the influences of the change of physical sizes and material parameters of fuzz-button connector on circuit impedance were analyzed based on time domain reflectometry (TDR) and high frequency parameters. This research provides a better understanding of the effects of physical dimensions and dielectric materials of fuzz-button connector on signal transmission and guides engineers in the selection of the proper parameters to ensure interconnections with high signal integrity.