Superconducting microstrip line model studies at millimetre and sub-millimetre waves

This paper presents results of superconducting microstrip transmission line simulation for the frequency range 100-1100 GHz. The simulation is used to calculate the characteristic impedance and the wave propagation constant in a superconducting microstrip line having different geometry. Indeed, modelling provides the only tool for designing superconducting microstrip - based circuits at millimetre and sub-millimetre wavelengths because no direct measurements of such a line can be made at this wavelengths and at cryogenic temperature of 4 K with ultimate accuracy. Niobium, as the most commonly exploited superconducting material, was used for the modelling, though the same approach would work for any different BCS1 superconductor. In order to evaluate the model accuracy, we have made an extensive comparison study of the superconducting microstrip models known from earlier publications, performed numerical simulations using 3D EM - solver, HFSS, and used a new model introduced in this paper with all simulation result plotted in the paper.