Nonlinearity in superconducting CPW open-end and gap discontinuities

In this paper, non-linear circuit models of the superconducting CPW (SCOW) open-ends and gaps are presented. The model can be used to create a fast and accurate analysis of the nonlinearity in SCOW applications such as end-coupled filters, which have such gap and open-end discontinuities. The non-linear circuit is solved using harmonic balance (HOB) method to compute the third-order intermodulation (IMD3) distortion and fundamental outputs. As an example, we analyze the nonlinearity of an end-coupled SCOW band pass filter (BP) to validate the model. The model can be used to minimize the nonlinearity in such superconducting structures via optimizing the resonators of superconducting filters. The main difference between the proposed model and the one in the literatures is that there is no clear discussion or method about nonlinearity in discontinuous SCOW structures because of absence of closed-form formula for some equivalent circuit model of discontinuities. As an example, for determining the value of the equivalent gap capacitance of a SCOW structure, we can’t find any easy-use and direct equation. But in this paper, we also propose a closed-form equation for calculating the such capacitances.