Lumped-element switchable superconducting filters

A switchable superconducting band-stop filter consisting of a series of LC resonators is described. Each resonator can be switched on or off using a bias current to control the superconducting-to-normal resistance transition. The bandwidth of the filter can thus be varied in steps. In each LC resonator, the magnetic field of the inductor passes through the fingers of the interdigital capacitor, and so a simple model is developed for the combined structure. The LC sections are placed in a coplanar line, but the model can easily be adapted to other types of transmission line. Experimental results are given