A Novel Nonlinear Model for Passive Intermodulation in Coaxial Connectors

A novel nonlinear model describing the passive intermodulation (PIM) behavior in coaxial connectors is developed based on sine function. Two types of coaxial connectors are selected as test samples, and a series of two-tone PIM tests are conducted. The coefficients of the sine function model for these connectors are obtained by fitting the test results using ordinary least squares (OLS) method. The predicted results of the sine function model agree well with the test results, which prove that the sine function model can be used to describe the third-order and the fifth-order PIM performance of coaxial connectors accurately. The differences between the sine function model and other nonlinear models are compared.

I. Introduction

Passive intermodulation (PIM) is a kind of signal distortion caused by the slight nonlinearity in passive devices. Coaxial connector is one of the major nonlinear sources of PIM in radio frequency communication systems. The nonlinearity of passive devices can be described by a nonlinear mathematical model. Polynomial model is an extensively used nonlinear mathematical model to describe the nonlinearity of coaxial connectors [1]–[10] and other passive devices [3], [11]–[14]. Some researchers adopted hyperbolic tangent function model to predict the behavior of PIM products in coaxial connectors [1], [4], [15]. Several nonlinear models based on the exponential function were proposed in order to characterize the nonlinearity of passive components in some investigations [4], [16], [17]. The studies mentioned above well summarized the nonlinear model of passive devices. The purpose of this letter is to develop a novel nonlinear model based on sine function to accurately describe the third-order and the fifth-order PIM performance of coaxial connectors.