Dual-mode filter with asymmetric response using square loop resonator DGS

This paper presents a novel dual-mode filter with asymmetric frequency response making use of square loop resonator DGS. Unlike the conventional dual-mode structure, the square ring resonator with a square patch attached at the corner is placed on the bottom plane, which is coplanar with the defected ground. Two T-shaped orthogonal feed lines are arranged on the top plane, which have an overlapped area with the resonator to excite and couple two degenerate modes. The proposed filter is found to have two transmission zeros on the high side of passband and takes on an asymmetric filtering property. Finally, a compact dual-mode square loop resonator DGS filter is designed and fabricated to operate at 2.68 GHz and its predicted results are verified in experiment.