Polynomial model for high-order and multi-carrier passive intermodulation products

Passive intermodulation (PIM) often limits the performance of communication systems, particularly in the presence of multiple carriers. Since the origins of the apparently multiple physical sources of nonlinearity causing PIM in distributed circuits are not fully understood, the process of PIM generation is frequently described by the behavioural models. In this paper, a memoryless nonlinear polynomial model, capable of predicting high-order multi-carrier intermodulation distortion, is deduced from the measurements of the third-order PIM products generated by two-tone carriers on a microstrip transmission line with distributed nonlinearity. The devised model is incorporated in Keysight Technology's ADS simulator to evaluate the adjacent band power ratio for three-tone signals on the transmission line with passive distributed nonlinearity. The obtained results suggest that the PIM distortion caused by multi-carrier signals can be reasonably estimated by simulation tools based on the behavioural models extracted from the conventional two-tone PIM tests.