Highly Selective Bandpass Filters Based on Miniaturized Dual- and Triple-Mode Patch Cavities

In this letter, miniaturized dual-mode (DM) and triple-mode (TM) patch cavities are proposed by using multiple capacitive-loaded patches (CLPs). The characteristics of the proposed new patch cavities are analyzed in detail for multiple-mode filters’ design. First, a single-cavity patch filter’ structure is proposed, which can realize DM and TM filtering responses. Then, a four-pole filter using two cascaded DM patch cavities is proposed. The proposed filters can realize quasi-elliptic responses with highly selective skirts. For the demonstration, two design examples are fabricated and measured. Compared with the traditional patch filters without CLPs, the size of the proposed patch filters can be reduced by 73.2%. The proposed multiple-mode patch filters have the merits of high selectivity and compact size.