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Abstract

This paper presents the design of new miniaturized multiband microstrip bandpass filters (BPFs) for multi-services wireless applications. The introduced filter structures are the results of the implementation of the fractal-based topology together with the stepped impedance resonator (SIR) technique on the conventional square loop resonator. Three microstrip BPFs have been investigated corresponding to the first three Minkowski fractal iterations as applied to the SIR ring resonator. The first bandpass filter, which corresponds to the zero fractal iteration, has been designed at 5.8 GHz for wireless local area network (WLAN) applications. The proposed filter has been etched using a substrate with an insulation constant of 10.8, a thickness of 1.27 mm and loss tangent of 0.0023. Based on this filter, the other two filters have been designed by applying the Minkowski fractal geometries of the 1st and 2nd iterations. Results reveal that the three filters offer size reduction percentages of about 40%, 56%, and 63% as compared with the conventional dual-mode square ring resonator. The simulated and experimental results of the first BPF prototype are well-matched.