Wideband Dual-Mode Microstrip Filter Using Short-Ended Resonator With Centrally Loaded Inductive Stub

In this paper, a new class of wideband filters utilizing a novel dual-mode resonator is presented. For the first time, the resonator realized by loading an inductive short-circuited stub at the center of the short-ended resonator is proposed. The inductive stub is tuned to control the filter bandwidth by splitting two degenerate modes. For wideband application, source-load coupling, which is introduced to compensate the insufficient I/O coupling strength in a parallel-coupled microstrip line, not only improves the property within the passband, but also produces transmission zero to enhance passband selectivity. In addition, the method of extraction of the source-load coupling coefficient is proposed, and through equivalent circuit topology analysis, three types of dual-mode wideband filters, by utilizing the proposed basic resonant unit and connecting two or three short-circuited points, are designed and fabricated with good performance.