Thin bandpass filters containing sections of symmetric strip transmission line

Thin (1-mm thick or thinner) combline bandpass filters based on sections of symmetric strip transmission lines and containing closely spaced (0.1–0.2 mm apart) stepped-impedance resonators are described. It has been found that, if these filters are made on high-permittivity ceramic substrates, their dimensions prove to be smaller than the dimensions of other ceramic-based filters. Various frequency characteristics of these filters—symmetric, with increased one-sided selectivity, and with a constant delay time—have been analyzed. The experimental results obtained for a 1-mm-thick bandpass filter with ? _r = 9.7 are in good agreement with the computer-simulation data.