Dual-band bandpass filter with rectangular shaped defective ground structure

A rectangular shaped defective ground structure (DGS) is proposed to enhance the response of an existing design of a dual-band bandpass filter topology. In this paper, the filter design is based on parallel-coupled lines connected to transmission lines. The filter consists of characteristics impedances of the transmission line represented by Zr, even-mode, Zre and odd-mode, Zro. The variation of the DGS positions and dimensions are realised and the effects on the response of the filter are analysed. It is found that an implementation of a rectangular shaped DGS in this topology improves the steepness of the response for both bands with centre frequencies at 1.22 GHz and 2.62 GHz. The optimised length and width of the DGS are 42 mm and 11.25 mm respectively, positioned at the upper and bottom centres of the ground plane. The simulated and measured results of the filter are compared where good agreement is achieved.