The RF front-end stage of the communication system is composed of passive devices such as a filter, a duplexer, a power combiner, an RF connector, and an RF switch. These passive devices are designed to maintain the possible linear characteristics in the operating range, but they have practically nonlinear characteristics. Passive intermodulation occurs when two or more different frequencies are used as inputs to a passive device having nonlinear characteristics. This phenomenon is called Passive IM (PIM). Intermodulation (PIM) signals are added as unwanted noise to an uplink band in a mobile communication system, which is a major noise source that deteriorates the signal to noise ratio (SNR). Therefore, the intermodulation (PIM) signal, which may cause a lot of losses in terms of operation, maintenance, and frequency use efficiency of the mobile communication system equipment, should be removed.

A system for removing an intermodulation (PIM) signal existing in an uplink band of a mobile communication system is called a PICS (Passive Intermodulation Canceller System).