Experimental investigation of a dual band-reject filter using C-shaped DGS with improved Q-factor

A compact, small size dual band-stop C-shaped defected ground structure (DGS) is proposed in this paper. Two similar C-shaped patterned ground structures are designed and their dimensions are adjusted to obtain band rejection frequency response at 2.4 GHz and 6.7 GHz. Then, two DGSs structure are cascaded in series to obtain a high Q-factor dual-band rejection property. The distance between two DGSs is adjusted for an acceptable response. All structures are numerically investigated using HFSS and the dual band filter is designed and implemented. Results show that there are two parallel resonance frequencies at 2.468 GHz and 6.629 GHz with a very high Q-factor, while signal attenuation at the resonant frequencies is at least 20 dB. Also, the equivalent circuit of the proposed filter including two parallel resonance RLC circuit based on measured S-parameters is presented. The new introduced DGS filter is successfully designed and fabricated and the measured results are in a good agreement with those obtained by numerical investigation.