Modified spiral shaped defected ground structure with spurious free band rejection performance

A modified spiral-shaped Defected Ground Structure (M-DGS) loaded on Coplanar Waveguide (CPW) transmission line is proposed in this letter. By removing the inner spiral turns from the conventional spiral-shaped DGS (C-DGS), spurious-free band-stop performance is achieved in a wide passband. The final testing structure cascaded six M-DGS cells to enhance the band-rejection behavior. Repeated measurements show that the notch depth is greater than -50dB at 3.64GHz within an area of 1.5 by 13mm ² . Insertion loss is under 3dB with no other harmonics up to 10GHz. For comparison purposes, C-DGS test structures with different numbers of removed spiral turns are also designed to validate the theory that the resonate frequency of a spiral-shaped DGS cell is dominantly controlled by the outermost spiral turn and each inner spiral turn contributes to the harmonics as well as some effect on the resonant frequencies and bandwidths.