New Compact Bandpass Filter With Tuning Stubs Based on 2nd Iteration of Hilbert Fractal Geometry

Abstract

A novel design of miniaturized microstrip bandpass filter is presented for use in modern wireless communication systems. The proposed filter structure is composed of dual fractal-based microstrip resonators. The structure of each resonator is in the form of the Hilbert fractal curve geometry. Two single-mode resonators with structures based on the 2nd Hilbert fractal-shaped geometries have been modeled at a design frequency of 2.4 GHz (ISM Band). The resulting filter structures based on these resonators, show considerable size reduction compared with the other microstrip bandpass filters based on other space-filling geometries designed at the same frequency. Another set of bandpass filter designs based on the same resonators but with a tuning stub has been also presented, in an attempt to provide practically useful means to tune the filter to the specified performance with a considerable tuning range. The performance of the resulting filter structures has been evaluated using a method of moments (MoM) based software package, Microwave Office 2007, from Advanced Wave Research Inc. Results show that the proposed filter structures possess fine return loss and transmission responses besides the size reduction gained, making them suitable for use in a wide variety of wireless communication applications. Furthermore, performance responses show that the second set of filters, based on Hilbert shaped resonators support the 2nd harmonic suppression