A compact tri-band bandpass filter using novel stub-loaded resonator

In this letter, a compact tri-band bandpass filter (BPF) using novel stub-loaded resonator is proposed. The resonator consists of one short stub and four open stubs which are symmetric about the middle open stub. Two coupling gaps were formed by the four bended open stubs, which contribute to the performance of second and third passband. The filter was designed, fabricated, and measured. Three passbands were designed to operate at 1.0, 2.4, and 3.5 GHz, respectively. The measured results of the tri-band BPF exhibit a reasonable agreement with simulated results. The circuit only occupies 0.106 λg × 0.064 λg, where λg is the guided wavelength at lower passband center frequency. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2797–2800, 2015