Miniaturized signal-interference planar filters

This paper addresses, for the first time, the development of miniaturized-size signal-interference planar filters. In particular, capacitive-loading and meandering-line techniques are simultaneously applied to decrease their occupied area. Footprint reduction, transfer function narrowing, and increased insertion loss caused by the capacitive loading are carefully considered for single- and multi-band bandpass filters (BPFs). Line meandering enables further size reduction in these circuits without coupled-line stages, since spurious-coupling effects become less critical. A 1-GHz miniaturized two-stage BPF prototype based on the hybrid-ring-type transversal filtering section (TFS) is built and tested to experimentally validate the presented concepts. This BPF prototype is nearly 4× smaller than its classic counterpart.