New microstrip bandpass filters with increased upper rejection band

Abstract

Microstrip bandpass filter (BPF) is one of the most important components in wireless communication systems. Unfortunately, without special measures, most of the BPFs exhibit harmonic responses that degrade the system performance. To overcome this problem, various methods have been reported [1]-[10]. Among them, modification and perturbation to the width of the coupled-line resonators are the most widely used approaches [1]-[4]. However, these methods focus on only second harmonic suppression. To obtain wide-stopband, stepped-impedance resonators (SIRs) are proposed [5]-[7]. In [5]-[6], SIRs with high frequency ratios and proper tapping locations are utilized to obtain wide-stopband. In [7], a combination of different SIR structures with the same fundamental resonant frequency but diverse spurious resonances is adopted for spurious-free BPFs. © 2010 IEEE.