Compact Stub-Coupled Square Open-Loop Bandpass Filter for Ku-Band Applications

Abstract

A typical stub-loaded compact planar microwave square open-loop based bandpass filter (BPF) is proposed in this paper. The internally loaded stubs are open and attached type accommodated inside the square loops. A large coupling coefficient value can be possible in the square open-loop resonator using those loaded stubs. The open loaded-stub is a modified stepped-impedance resonator (SIR) structure, and the attached stubs are two similar and rectangular structures. By integrating the three loaded stubs into the two squareloops using open gaps and employing direct-connected asymmetrical feeders, the combination of such structures excites the resonator filter at 12GHz resonant frequency which is applied to get bandpass filter with wideband passband response with high input reflection coefficient. The proposed open-loop filter structure has strong electric coupling because the open sides of two coupled loop resonators are proximately placed face-to-face in parallel. The internally loaded stubs help to connect magnetic coupling easily. Therefore, the mixed coupling generates strong electromagnetic coupling in the BPF with high input reflection coefficient and broader bandwidth on the required frequency band. The S-parameters responses of the fabricated filter nearly match the electromagnetic simulation results. Therefore, the feasibility of the proposed filter is approved.