The compact 3‐stage 2.4/5.2 GHz bandpass filter with modified winding hairpin structure and insert coupling

Abstract

Two hairpin resonators, one ''Z-type'' modified steppedimpedance resonator, and two transmission lines are composed to design the compact and miniature dual-band bandpass filters (BPFs). The designed BPFs are presented to operate at 2.4/5.2 GHz for industrial, scientific, and medical (ISM, 2.4 GHz) and WLAN applications (2.4/5.2 GHz) without additional impedance matching network. The 2.4 GHz and 5.2 GHz dual-band can be simultaneously excited and tuned by adjusting the electric length ratio (h) and characteristic impedance ratio (K) of resonators. Cascaded arrangement is designed for wide bandwidth and high out-of-band rejection, and the ''Z-type'' resonator and insert coupled modification are used to increase the utility rate of space and reduce the size of designed filter. Al 2 O 3 ceramic with thickness of 0.635 mm and dielectric constant of 9.4 used as the substrate, and the designed filters are fabricated by printing method. Because of higher dielectric constant substrate and modified structure, the proposed filters show the advantages of wide bandwidth, low insertion loss, high out-of-band rejection, simple circuit, and tiny size.