Novel Compact Microstrip Stepped-Impedance Resonator Using Computational Approach and Application to Dual-Band Bandpass Filters

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 3f1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$3\hbox {f}_{1}$$\end{document}, 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.