Compact dual-wideband bandstop filters based on open-coupled lines and transversal signal-interaction concepts

Two compact dual-wideband bandstop filters based on open-coupled lines and transversal signal-interaction concepts are proposed in this study. Two transmission paths with a half-wavelength open stub and two open-coupled lines are used to realise two wide stopbands for WLAN bands. Second/third-order stopbands with transmission poles near each stopband can be easily achieved by the two transmission paths. Two planar dual-wideband bandstop filters with 10 dB fractional bandwidths of 40 and 18.2, 61 and 26.8% are designed and fabricated. The theoretical and measured results are in good agreement and show good in-band filtering performance and high selectivity.