Phase Compensation of Cascaded Conductor-Backed CPW Periodic Cells

Several unit cells of conductor-backed coplanar waveguides with and without loading using thin-film ceramic technology are investigated. The frequency-dependent lumped equivalent circuit values of the cells are extracted from the full-wave electromagnetic analysis. Slow-wave periodic transmission lines and end-coupling bandpass filters (BPFs) are designed, fabricated, and measured. Size reductions of 23% and 27% for the loaded filters and several times increase of inverter values for the coupling inverters are achieved compared to that for the unloaded ones. A systematic design method by using cell cascading with compensation is proposed for the designs of the lines and filters. It is also demonstrated that “finite ground,” used in conductor-backed coplanar waveguides in the literature, is no longer suitable for the end-coupling BPFs due to the leakages. The leakages of finite ground deteriorate the stopband rejection of filters as much as up to 32 dB compared with that of “via ground”.