This paper discusses a novel multi-stub-loaded stepped-impedance resonator (MSLSIR) with a specific feeding structure. The fundamental and higher order modes of resonant frequencies of the stepped-impedance resonator are key parameters involved in the design of a dual-band bandpass filter (DBPF). However, since resonant frequencies are dependent on each other, the overall structure is not compact. The proposed MSLSIR has the advantage of flexible control over one resonant frequency while the other frequency is fixed. Furthermore, the utilization of isosceles right-angled triangular (IRT) and short-circuited stubs as loaded elements improves size miniaturization of DBPF when a low permittivity substrate is used. The analysis of the IRT stub is based on the coupling impedance formulas derived by integration of the associated Green's function. As an application, a DBPF is presented, which operates at 3.5 and 5.2 GHz, corresponding to the WiMAX and WLAN applications, respectively. In addition, a good stopband rejection, up to 3f 1 , is obtained using the defected ground structure technique. An overall good agreement between the calculated, simulated and measured results is observed, thereby confirming the effectiveness of the proposed method.

In this article, a novel compact microstrip dual-mode multistub-loaded stepped-impedance resonator is introduced. Steppedimpedance resonator can be used for achieving the fundamental resonance frequency; however, the size of this structure is not compact and resonance frequencies are dependent. Utilizing multistubs as loaded elements improves size miniaturization with low permittivity substrate and brings the advantage of flexible controlling of one resonance frequency whereas the other one is fixed. As an application, a dual-band bandpass filter is presented to operate at 3.5 and 5.2 GHz, corresponding to the worldwide interoperability for microwave access and wireless local area network applications. An overall good agreement between the measured and simulated results is observed, confirming the proposed method.