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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”.
Components, Packaging and Manufacturing Technology, IEEE Transactions on (Volume:2 , Issue: 9 )
Date of Publication: Sept. 2012