Communication Nonlinearities Techniques for Analysis of Passive Intermodulation

This paper is concerned with characterisation of passive intermodulation (PIM) in distributed RF circuits and components with the aid of emerging nonlinear RF techniques. Conventionally, intermodulation (IM) is defined as a phenomenon which is characterised by the appearance of additional spectral components in the output spectrum of a nonlinear system different from the carrier frequencies. The IM products occurring in the Tx or Rx bands can cause intolerable signal distortion. In the frequency division duplexing (FDD) systems, the Tx/Rx IM distortion results from the nonlinear mixing of the Tx signals and manifest themselves as the IM products in the Rx band. With respect to the transmitter IM, the IM products in the Tx band, which may, for instance, originate from amplifier nonlinearity, appear as either intrachannel or interchannel nonlinear interference. In the multi-band and co-located systems, the products of the nonlinear mixing of the Tx signals from arbitrary bands can fall within any Tx or Rx band. In general, the Tx signals are modulated, which adds to complexity of the IM analysis, since the bandwidth of the IM products scales up with the their order. Ultimately, the IM products debilitate the receiver sensitivity and data throughput in wireless communications systems.