Design of Compact Bandpass Filters based on Fractal Defected Ground Structure (DGS) Resonators

Modified Minkowski fractal geometry has been found to be attractive for microwave circuit designers because of its high space-filling property. This property will lead to the design of compact circuits; meeting the requirements of the modern communications systems to be with small size. In this paper, the design of a compact microstrip BandPass Filters (BPF) has been proposed based on the modified Minkowski fractal (DGS) resonators. The proposed BPF structure is composed of two coupled resonators etched as fractal DGS structures. Results reveal that as the iteration level of fractal based DGS becomes higher, more compact filter structure will result in. Furthermore, the presented DGS structures with fractalshaped resonators can be adopted to design compact planar BPFs with reasonable performances. The performance curves offered by the resulting filters are characterized by the low loss across the passband and high rejection levels outside it with steep roll-off in both edges of passband. Measured results of a fabricated prototype of a 2nd iteration fractal DGS BPF have shown reasonable agreement with those predicted by simulation. Measured results of a 2nd iteration fractal DGS BPF have shown satisfactory agreement as compared with simulation results. There is a slight shift of the lower edge of the passband response of the transmission characteristics, while the upper edge is s very close. The results have shown that the filter has reasonable performance characteristics with considerable reduction of higher harmonics. The compact size of the proposed filter together with the realized high selectivity will make it suitable for a broad range of the recently available wireless communication services.