Effective notch Ultra-Wideband filter using ring resonator for the rejection of IEEE 802.11a

This paper proposes Ultra-Wideband (UWB) bandpass filters with dual notched 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 ring 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 band(s) by tuning the ring size with respect to interdigital coupling. Design of the UWB bandpass and notch filters are proposed and group delay has also been obtained for both filters in this paper. The proposed filters presented both excellent ultra-wide bandwidth from 2.2 GHz to 10.5 GHz and rejection performance about -23 dB and -20 dB with centre frequencies at 5.3 GHz and 5.8 GHz respectively for notched band filter. The proposed filters have also shown good outband performance that is better than FCC´s (Federal Communications Commission) mask.