Design of Compact Tri-Band Bandpass Filter using λ/4 and Stub-Loaded Resonators

This paper presents a novel approach for designing triband bandpass filters with independently controlled center frequencies and bandwidths. λ/4 and short stub loaded resonators are employed to obtain tri-band responses. λ/4 resonators are designed to operate at the third passband, and stub-loaded resonators are designed to operate at the first and second passbands. The bandwidth of each passband can be tuned independently by adjusting the coupling gaps or lengths. A tri-band filter was designed and simulated to verify the presented concept, the filter achieved insertion losses of 1.4, 1.8 and 1.8 dB at 2.4, 3.5, 5.5 GHz, respectively.