Asymmetric Coupled-Resonator Bandpass Filter for Ultra-Wide Stopband

The research presents a novel combination of an asymmetric coupling with a stepped impedance resonator (ACSIR) to realize high performance bandpass filter, especially an ultra-wide stopband rejection.A basic secondorder bandpass filter was developed and subsequently extended to a fourth-order configuration to improve key performance metrics, including wide stopband characteristics and compact size, without compromising insertion loss.The use of asymmetric coupling enables optimization of the filter response while preserving a simple configuration.Furthermore, the resonance conditions associated with the asymmetric coupling were examined through mathematical analysis.The proposed ACSIR filter achieved an enhanced fractional bandwidth (FBW) of 15.4%, a low insertion loss of 0.64 dB, and wide stopband rejection extending up to 7.25 f 0 tailored for WLAN applications operating at 2.45 GHz.