Effects of Mechanical Design on Passive Intermodulation in Coaxial Connectors

Passive intermodulation (PIM) is a thorny issue that exists in a wide array of coaxial connectors at high frequency. One important factor in the occurrence of PIM interference are the details of the mechanical design of a given coaxial connector. Accordingly, characterizing the impact of such effects on PIM provides both improved technical understanding and analysis tools for the optimization of a connector's mechanical design for the minimization of PIM. In the present work, the effects of the mechanical design on passive intermodulation in coaxial connectors were investigated using both modeling and experimental testing. The effects of both the geometrical length and angle of coaxial connectors were analyzed. Based on transmission line theory, an equivalent circuit model of varying geometrical length was developed. Considering the signal reflection at the angle, the coaxial connector was treated as equivalent to an unmatched transmission line, and an equivalent circuit model of varying geometrical angles was also developed. SubMiniature version A (SMA) connectors fabricated with different lengths and angles were selected as experimental samples and PIM tests were conducted to validate the models and analysis results. The experimental measurements show good agreements with the simulation results. Analysis of the results provide insight into the conditions for which mechanical design considerations may be a significant driver of PIM in connector systems. The techniques developed and demonstrated in this study provide tools and procedures that may assist in evaluating and improving PIM performance in proposed connector designs.