Lowpass filter with slow-wave rail coplanar stripline (R-CPS)

The coplanar stripline (CPS) suffers from excessively high characteristic impedance which makes the design of filters difficult. Proposed is a slow-wave rail CPS (R-CPS) transmission line for the design of a stepped impedance lowpass filter. The R-CPS exhibits an extended low-impedance limit not achievable by conventional CPS, while retaining the advantages of the CPS. It also improves the performance of the filter in terms of suppression of the spurious harmonic passbands and reduces the filter size.