Simulation of the effects of the residual low level PIM to improve payload design of communication satellites

The passive intermodulation (PIM) is a well known inconvenience in satellite links. It consists in an unwanted generation of harmonics and resulting intermodulation products in weak nonlinear components crossed by RF currents or in irradiation of these unwanted signals by external materials exposed to a strong RF electromagnetic field. Several studies have been carried out to reduce this negative effect and particular measurement techniques have been employed in pre-launch testing of the whole components of the required payload. The extension of the satellite links to mobile communications, which require more transmitted power and increased receiver sensitivity, renders more and more important the reduction of the PIM effects on the downlinks to obtain a satisfactory level of quality of service (QoS). This paper reports the simulation results of effects of the third order PIM products in a multichannel transmitting system. The simulations are carried out by using time-frequency representations of the unwanted combinations of spurious signals generated by third order PIM products. The results of the above simulations are interpreted and a first attempt of design guidelines is given.