Investigation in Open Circuited Metal Lines Embedded in Defected Ground Structure and Its Applications to UWB Filters

A novel method for notch implementation in ultrawideband (UWB) bandpass filter (BPF) using open circuited metal lines embedded in a defected ground structure (DGS) is proposed. Distinct from traditional notch implementation, the proposed method uses the additional metal lines with half waveguide length embedded in defected ground structure to produce additional notch band behavior based on the DGS bandpass behavior. Furthermore, the equivalent circuit model of the proposed UWB BPF with notch implementation is established for explaining the circuit behaviors more explicitly. In this way, the proposed circuit has a very small size, only amounting to 0.41 by 0.22 guided wavelength at the center frequency of 6.85 GHz. The experimental filter has a notch band frequency of 5.5 GHz, with two observable attenuation poles at 1.65 and 11.36 GHz, respectively. The measured BPF insertion loss is less than 1.0 dB throughout the passband of 3.1 to 10.6 GHz, and the variation of group delay is less than 0.2 ns in this band, except for the notched band.