Analysis of passive intermodulation in cascaded connectors with transmit‐receive systems

Abstract

Passive intermodulation (PIM) is usually expressed by the third‐order intermodulation power excited by two‐tone signal, which has limitations in characterising nonlinear distortion of signal in actual communication system. The effect of PIM on modulated signals are analysed at both the transmit and receive port with multiple passive nonlinear sources. Four types of coaxial connectors are adopted to represent four different levels of PIM. The equivalent circuits of PIM sources in series or parallel are proposed. With the circuit simulations and theoretical modelling, the effect of PIM on the analog and the digital modulation signals are analysed respectively. Two indexes of adjacent channel leakage ratio and error vector magnitude are modelled, showing the PIM effect at transmit port. A system model of a transmit‐receiver is provided, investigating the effect of PIM on the symbol error rate in a receiver. The effects of PIM distortion on different modulated signals are observed both in experimental measurements and simulation tests, verifying the theoretical models.