Theoretical Analysis of Superconducting Submillimetre Wave Microstrip Transmission Line

The behaviour of superconducting microstrip transmission line has been investigated by a number of authors [1, 2]. The techniques used range from conformal transformations through to complete full-wave analyses. Despite this work, it is still difficult to know which approach should be used for designing submillimeter-wave circuits, and indeed the degree to which the various approaches agree. Clearly, every method has its strengths and weaknesses, and to some extent the suitability of a technique depends on the particular application being considered. Clearly, an important consideration is the ease with which a procedure can be used. It might be argued, for example, that full-wave analyses are best, but such calculations require large computers and are slow to use. In many cases simple closed-form expressions may give the required degree of accuracy. Moreover, it is often important to be able to analyse the behaviour of circuits working at frequencies close to the gap and at temperatures approaching the critical temperature; in these cases it is desirable to use a simple perturbation approach which can be integrated with standard methods for characterising the surface behaviour of superconductors.