Dual High-Selectivity Band-Notched Ultra-Wideband Filter with Improved Out-of-Band Rejection

A novel microstrip ultra-wideband (UWB) filter with dual notched bands is presented. By placing a simple dual-mode resonator having two symmetrical outer high-impedance lines beside the UWB filter, two controllable rejection bands are created, each of which features two resonant modes and high frequency selectivity. Defected ground structure techniques (DGS) is applied to realize wide out-of-band attenuation. To explain band-notched operating mechanism, the parametric studies and equivalent circuit of the proposed structure are presented. The experimental results agree well with the predicted results declaring the advantages of the proposed structure with high-selectivity widebandwidth notched bands and improved out-of-band rejection.