Ultra-wideband bandpass filter with dual notched bands using hybrid microstrip/CPW structure

A novel ultra-wideband (UWB) bandpass filter (BPF) with dual notched bands using the hybrid microstrip and coplanar waveguide (CPW) structure is proposed, to prevent interference problems between the UWB radio system and existing radio systems. A multiple-mode resonator on a CPW is formed to allocate its first three resonant modes around the lower-end, centre and upper-end of the 3.1 to 10.6 GHz UWB passband. Its two sides are fed by two microstrip-to-CPW transitions with enhanced frequency-dispersive coupling degree. The dual narrow notched bands are introduced by embedding a open stub in the CPW line and etching two U-shaped slots on the ground plane to form defected ground structures (DGSs) in each side of the microstrip structure. Then, dual-band rejected filtering properties in the C-band (3.7-4.2 GHz) and WLAN (5.15-5.825 GHz) are achieved. The UWB bandpass filter with notched bands has been carried out by designs and related simulations to demonstrate the notch-band-included and upper-stopband-improved performances.