| Popis: |
The passive nonlinearities in wireless communication systems and devices, which manifest themselves in passive intermodulation (PIM) distortion of the receive signals in frequency division duplex and multi-radio systems. This study is devoted to investigation of PIM effects in distributed microwave circuits and materials in order to develop efficient modelling approaches and a means of PIM mitigation. Review of the existing methodologies indicates the acute need of new efficient software and hardware tools, and techniques for reliable characterisation of the PIM sources and mechanisms of PIM generation in microwave components. The methodology of this work is essentially based upon the modern nonlinear system analysis, which proved to be successful in applications to the power amplifier nonlinearities and transceiver linearization. We adopt and advance a rigorous theoretical framework based on the harmonic balance analysis of nonlinear transmission line and X-parameters formalism enabling an accurate modelling of cascaded and distributed nonlinear circuits. The developed approach is efficiently implemented in the RF design software, such as Keysight ADS, to provide for detailed characterisation of passive distributed nonlinearities and analysis of signal distortions. Our experimental studies have yielded a number of valuable insights in the nature and causes of lumped and distributed passive nonlinearities in printed microwave circuits and devices. The experimental techniques of PIM characterisation, i.e. two-port PIM measurements and near-field probing, have been advanced through the research presented in this thesis to become reliable and practical tools. The developed theoretical approach has been applied to modelling passive distributed nonlinearities and PIM distortion of the received signals in printed transmission lines with electrical discontinuities. The work in this thesis offers new analysis and experimental methods and offers insights that guide the way for new PIM-free technologies that utilise microwave materials, components and systems, as well as new standards of PIM characterisation and modelling. |
