Development of UWB dual notch filter to reject IEEE 802.11a using ring resonator

A new Ultra-Wideband (UWB) dual notch filter is developed and studied for the purpose of reducing interference from the WLAN (802.11a) when it coexists with the UWB radio system. The filter is based on ring resonator with interdigital coupling at both sides. The interdigital coupling is used instead of direct coupling for the reason of strong coupling and to introduce capacitance effect to obtain flat passband. The notched band is designed to reject the both lower (5.15-5.35 GHz) and upper (5.725-5.825 GHz) bands of WLAN by introducing four open stubs at the coupling arms nearby the ring geometry. The dual notch is obtained at 5.1 GHz with -20 dB and at 5.9 GHz with -9 dB and group delay variation under 0.05 ns over the -10 dB operating band of 5.56 GHz. The overall size of the designed filter is 6 mm (length) × 39.2 mm (breadth) × 1.6 mm (height). The phase of S21 throughout the passband of presented filter is acceptably linear for UWB applications.