High-Selectivity Bandpass Filters With Low Loss and Reduced Size Based on HCILA Slow Wave Technology Encapsulated in Patch Cavities

In this letter, novel low-loss and reduced-size single-and dual-mode (S-DM) slow-wave rectangular patch resonators (SWRPRs) are proposed based on a hybrid capacitive-inductive-load array (HCILA). The SWRPRs are analyzed in detail, and a highly selective DM two-pole quasi-elliptic bandpass filter (BPF) is proposed. The in-band insertion loss (IL) and size of the BPF are significantly reduced due to the use of HCILA. Three- and four-pole BPFs are realized by S-DM SWRPRs, and the introduced additional finite transmission zero (FTZ) can be efficiently controlled by phase coupling. A four-pole BPF is designed, fabricated, and measured for the demonstration. Results indicate that the proposed patch BPF offers the benefits of reduced size, high selectivity, and low loss, thereby expanding the potential applications of patch circuits.