CAD techniques for superconducting millimetre and submillimetre-wave circuits

Over the last few years, considerable progress has been made in the development of techniques for fabricating high-quality superconducting circuits, and this success, together with major advances in the theoretical understanding of quantum detection and mixing at millimetre and submillimetre wavelengths, has made the production of CAD tools for superconducting nonlinear circuits an important new enterprise. A further motivation for modelling the behaviour of superconducting nonlinear circuits is that there is a range of circuits whose characteristics have not been studied in any detail. To model the behaviour of a quasiparticle mixer, it is first necessary to simulate the large-signal steady-state dynamics of the local-oscillator circuit. Once the large-signal operating point is known, it is then possible to perturb, either numerically or analytically, the underlying system of equations to gain information about the linear relationships between signal and noise variables. Clearly, if the simulator is to support advanced CAD facilities such as optimization, then it must be capable of calculating the large-signal behaviour of superconducting tunnel junctions efficiently