WLAN bandpass filter with wide stopband using spurlines and microstrip stubs

In this paper, a new microstrip open loop resonator bandpass filter (BPF) for wireless local area networks (WLAN) with wide stopband response is presented. The BPF consists of a pair of λ/2 open loop resonators and two additional resonators operating at the center frequency of 2.44 GHz. A novel resonator consisted of asymmetrical spurlines and quarter-wavelength open-circuited stubs are adopted at the input/output (I/O) feed lines to improve the stopband characteristics. The current distribution is demonstrated and analyzed. For the outband spurious respond suppression, its stopband attenuation loss is lower than -20 dB from 2.6 GHz to 10 GHz, and its insertion loss is as low as 1.05 dB. Good agreement is achieved between simulated and measured results.