Miniaturized microwave passive filter incorporating multilayer synthetic quasi-TEM transmission line

This paper presents a novel approach to miniaturizing a transmission-line (TL)-based bandpass filter (BPF). The BPF is miniaturized by incorporating multilayer stacked synthetic quasi-TEM TLs made of complementary conducting strip (CCS) metal surfaces. The stacked CCS TLs are separated by a meshed ground plane, whose coupling effect was experimentally shown negligibly to affect desired circuit performance. A brief description of the symmetric third-order TL filter synthesis procedure is reported to map such an idealized BPF to the prototype made of the stacked synthetic CCS TLs. Excellent agreement is obtained by comparing the experimental and theoretical filter frequency responses showing a 2.46-dB insertion loss, a -16.8-dB return loss with under 5% offset of low-side out-band transmission zeros, and a 2% offset of center frequency. A quick estimate of the proposed miniaturized filter design based on synthetic quasi-TEM lines shows that the particular filter prototype approaches the process limit.