The correlation between the placement of spiral defected ground structures in each ground plane of a grounded coplanar waveguide and the corresponding frequency response are investigated. S-parameters and current density plots from an EM-based simulation study are examined to understand this relationship. Simulation and measurement results show that the highest rejection is obtained when placing defected ground structures in both the top and the bottom ground planes. Furthermore, placing unique defects in both ground planes allows the design of dual-behaviour resonators.