Communication Nonlinearities Techniques for Analysis of Passive Intermodulation

The X-parameter based nonlinear modelling tools have been adopted as the foundation for the advanced methodology<br/>of experimental characterisation and design of passive nonlinear devices. Based upon the formalism of the Xparameters,<br/>it provides a unified framework for co-design of antenna beamforming networks, filters, phase shifters and<br/>other passive and active devices of RF front-end, taking into account the effect of their nonlinearities. The equivalent<br/>circuits of the canonical elements are readily incorporated in the models, thus enabling evaluation of PIM effect on the<br/>performance of individual devices and their assemblies. An important advantage of the presented methodology is its<br/>compatibility with the industry-standard established commercial RF circuit simulator Agilent ADS.<br/>The major challenge in practical implementation of the proposed approach is concerned with experimental retrieval of the X-parameters for canonical passive circuit elements. To our best knowledge commercial PIM testers and practical laboratory test instruments are inherently narrowband and do not allow for simultaneous vector measurements at the PIM and harmonic frequencies. Alternatively, existing nonlinear vector analysers (NVNA) support X-parameter measurements in a broad frequency bands with a range of stimuli, but their dynamic range is insufficient for the PIM characterisation in practical circuits. Further opportunities for adaptation of the X-parameters methodology to the PIM<br/>characterisation of passive devices using the existing test instruments are explored.