Open loop resonator bandpass filter with wide stopband using spurlines and microstrip stubs

This paper presents a new microstrip open loop resonator bandpass filter (BPF) for wireless local area networks (WLAN) with wide stopband response. The proposed BPF is composed of a pair of half-wavelength open loop resonators and two additional resonators operating at the center frequency of 2.44 GHz. Two novel resonators consisted of asymmetrical spurlines and quarter-wavelength open-circuited stubs are adopted at the input/output (I/O) feed lines to improve its stopband performance. For the outband spurious respond suppression, its upper stopband attenuation loss is lower than -20 dB from 2.6 GHz to 10 GHz, without affecting the center frequency and insertion loss. Good agreement between simulated and measured results.