On Optimum Design of Planar Microwave Components under Linearity Constraints

In this paper, we have presented a consistent approach to the nonlinear model assessment by means of conventional two-tone PIM measurements and efficient RF CAD simulations. Although the closed-form theoretical analysis can provide valuable insights in the effects of the physical and geometrical parameters, the underlying assumptions are often difficult to validate. Besides, analytical complexity rapidly grows for non-uniform and resonant circuits, which warrants the development of a more efficient empirical means of PIM characterisation and modelling. To that end, the RF CAD approach has been proposed to facilitate the nonlinear characterisation and PIM analysis of arbitrary circuit layouts and signals. Two examples of the microstrip filters based on the step-width discontinuities and shunt stubs have been presented and the simulation results confirm that PIM reduction is achievable by careful selection of the microstrip layout without frustrating the small-signal performance. Moreover, the presented simulation results are in a very good agreement with the experiments and published works, which suggests feasibility of improved PIM control in the future.