Compact fork stub-loaded square open-loop bandpass filter for VSAT applications

Abstract

A compact stub-coupled microstrip square open-loop resonator-based bandpass filter (BPF) is proposed.In this work, a back-to-back fork-shaped open stub and two attached stubs are internally accommodated inside the square loops using open gaps. Significantly, large coupling coefficient value can be obtained in the square open-loop resonator using those loaded stubs. In this design structure, the inserted stubs enhance to couple the two loops electromagnetically to each other. The proposed filter has strong electric coupling, because the open sides of the two coupled loops are proximately placed face-to-face in parallel. Similarly, the rectangular stubs attached with the internal wall of loops help to connect magnetic couplings between the two loops, as a result, the mixed coupling generates strong electromagnetic coupling in the BPF with an adequate input reflection coefficient and broader bandwidth in required frequency band. The open-loop BPF at 14.4 GHz is realized by an embedded open-stub combined with attach-stubs. The designed filter shows the simple topology, low insertion losses, and sharp rejections. The S-parameter response of the fabricated filter closely matches with the simulation results and, therefore, the feasibility of the proposed filter is confirmed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2412–2416, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27054