Analysis of the periodic superconducting CPW transmission line with stepped-impedance for on-chip microwave filter applications

Abstract

This paper investigates the filter properties of a superconducting coplanar waveguide (CPW) periodically loaded with stepped-impedances. The unit cell of the stepped-impedance filter is a cascade of two transmission lines (TLs) with different characteristic impedances. This impedance difference is obtained by step changing on the width of the center strip of the CPW. We use the ABCD matrix representation together with the Floquet analysis to derive the dispersion relation of the infinitely long periodic structure. Scattering matrix analysis along with impedance calculation is performed for an arbitrary number of unit cells. Complex propagation constant, scattering parameters and the input impedance of the structure are expressed in a closed-form equations. The results display the low-pass filtering property. Also, the effect of changing geometrical parameters on the cut off frequency, rejection bandwidth and attenuation in rejection band of such a filter are shown and discussed in this paper. © 2010 IOP Publishing Ltd.