UWB bandpass filter with notched band for the rejection of 5 GHz WLAN using hexagonal multiple mode resonator

This paper presents an ultra-wideband (UWB) bandpass filter for UWB applications and notch filter for the purpose of reducing interference from the WLAN (802.11a) when it coexist with UWB radio system. The bandpass filter consists of a hexagonal shaped multiple mode resonator (MMR) with interdigital coupling at both sides. The notch filter consists of four identical open ended stubs nearby the MMR which introduce a narrow rejection band in the UWB passband. Such UWB bandpass filter with notched band is useful and required in practical systems in order to avoid the interference from the existing WLAN to the UWB radio system. The analysis of the proposed filter is performed by using an electromagnetic (EM) solver, IE3D. The group delay obtained for bandpass filter is below 0.2 ns and for notch filter it is about 0.3 ns. With the above structural features the overall dimension of the filter is 38 mm (length) × 3.2 mm (breadth) × 1.6 mm (height) and the fractional bandwidth of the UWB bandpass filter is about 120.48% with return loss is about −40 dB.