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SUMMARYAn iterative method based on the wave concept is used to analyse a defect ground structure (DGS). In this case two applications are given. Firstly, we studied a l=4 bias transmission line maintaining high impedance that is added dumbbell-shaped DGS on ground plane of the conventional l=4 bias transmission line. Secondly, a newly etched DGS with a spiral shape in metallic ground is studied. The spiral DGS can provide steep rejection characteristics with one and two spirals. Numerical results are compared with published data, a good agreement is observed.