volume | PIER Journals

Abstract

A novel approach for designing planar dual-mode bandpass filters using symmetrical T-shaped stub-loaded stepped-impedance resonators (TSLSIRs) with high frequencies selectivity is presented. The proposed symmetrical TSLSIR structure is mainly composed of three elements, i.e. a stepped-impedance resonator (SIR), and two T-shaped stubs which symmetrically loaded at the middle sections of the SIR. Then, two dual-mode bandpass filters based on TSLSIRs with high frequencies selectivity are proposed for experimental verification. Firstly, a dual-mode single passband filter with two transmission zeros located at the both sides of passband is presented, whose passband is centered at 5.23 GHz with the fractional bandwidth of 10.1%, and a wide upper-stopband with harmonic suppression better than 20 dB in range of 5.9 GHz to 12.9 GHz is achieved. Secondly, a dual-mode dual-band bandpass filter with four transmission zeros located at the both sides of the two passbands is presented, whose two passbands are centered at 3.4 GHz and 4.54 GHz with the corresponding fractional bandwidth of 8.4% and 7.5% respectively, and the spurious frequencies from 4.9 GHz to 8.45 GHz are successfully suppressed to the level lower than -20 dB. Both filters have been designed, fabricated and measured. The measured results show good agreements with those of the simulation.

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Dr. Changhai Hu

Dr. Xiang-Zheng Xiong

Dr. Yan-Liang Wu

Dr. Cheng Liao