A novel prolate ellipsoid dual notch UWB filter for the rejection of 5 GHz WLAN

This paper proposes an Ultra-Wideband (UWB) bandpass filter with dual notch band for the purpose of avoiding the interference between the UWB radio system and the existing WLAN system. The 5 GHz WLAN (Wireless Local Area Network) IEEE 802.11a exists in 5.15-5.35 GHz and 5.725-5.825 GHz which are called as lower and upper band respectively. The filter is based on prolate ellipsoid resonator with interdigital coupling at both sides. The interdigital coupling used instead of direct coupling for the reason of strong coupling and to introduce capacitance effect to obtain flat passband. The notched band can be easily designed to some specific frequency bands by tuning the resonator size and four folded open stubs near by the ellipsoid resonator with respect to interdigital coupling. The proposed filter presented both -10 dB bandwidth from 1.69 GHz to 10 GHz and rejection performance about -20.29 dB and -18.80 dB with centre frequencies at 5.19 GHz and 5.79 GHz respectively. With the above functional features the overall dimension of the filter is 39.4 mm (height) × 7 mm (length) × 3.175 mm (breadth). It is not only compact but also delivers excellent scattering parameters with the magnitude of insertion loss, |S₂₁| lower than -1.7 dB and return loss better than -17.2 dB. In the passbands, the computed group delay is well within the tolerable variation of 0.1 ns.