Dual-Band Bandpass Filter with Dumbbell Shaped Defective Ground Structure

A dumbbell shaped defective ground structure (DGS) is implemented to improve the performance of an existing dual-band bandpass filter topology. The filter design is based on parallel-coupled lines connected to matched transmission lines. Various positions and dimensions of dumbbell DGSs are implemented and their effects on the filter performance are investigated. It is found that the utilisation of dumbbell shaped DGSs in this topology improve the steepness of the responses for the first and second passbands with centre frequencies of 1.365 and 2.932 GHz respectively. The optimised dimensions of the DGS are 5 x 5 mm2 for both its rectangular slots connected by a 0.5 mm narrow slot width. The optimised positions of the DGSs are located at the centre and the edges of the parallel-coupled lines. The simulated and measured results of the filter are analysed and discussed in this paper