Design of Compact Tri-Band Filter Based on Sir-Loaded Resonator with 0°Tapped-Feed Structure

Abstract

AbstractIn this paper, a novel compact tri-band filter based on SIR-loaded resonator is presented. By adding λ/4 resonators inside the SIR-loaded resonators, a compact tri-band filter is obtained. Three passbands are designed to operate at 1.85 GHz, 2.575 GHz and 3.05 GHz, respectively. The first and second passbands are established by utilizing resonator loaded with SIR, whose circuit size is much smaller than the legacy uniform impedance resonator (UIR). Then the λ/4 resonators are applied to generate the third passband. The three passbands can be adjusted to meet the requirements. The skew-symmetric (0-degree) tapped-feed structure is used to introduce a pair of transmission zeros, so the frequency selectivity is greatly improved. Due to the λ/4 resonators are embedded in the SIR-load resonators, the minimization of the tri-band filter is realized. A practical tri-band filter is fabricated and measured. The measured results show good agreement with the simulated ones.