The Design Of Microstrip Filter Based On DGS

Defected ground structure (DGS) was first proposed based on the theory of photonic band gap (PBG).In order to change the distributed parameters (distributed capacitance and distributed inductance) of the microstrip line, it etched defective graph on the ground plane of the dielectric substrate. The structure of DGS has a great advantage in enhancing the performance of filters for it’s simply structure with the characteristic of easy to be integrated and fabricated.The basic theory of designing microstrip filters and DGS have been introduced in this paper, some conventional structures of DGS are analyzing at the same time.The main work done in this thesis can be concluded as follows:(1) By analyzing several conventional structures of DGS, then the equivalent circuits of dumbbell DGS have been proposed and analyzed, the circuit simulation and electromagnetic simulation of dumbbell DGS have also finished respectively. The simulated result has proved the validity and feasibility of the extracting method of the DGS’equivalent circuit.(2) By introducing DGS of a group of symmetric split ring resonators to a conventional filter, a novel microstrip bandpass filter has been achieved. The simulated and fabricated results show:the center frequency of this filter is 4.5GHz, the relative bandwidth is 7%, and the return loss is lower than-12.5db.(3) By using nesting technology, a lowpass filter with band-notched characteristic has been achieved where the DGS of a group of cascade nested U-shaped slots is etched on microstrip ground. The simulated and fabricated results show this band-notched lowpass filter is working at the range from 8GHz-15GHz, the restrain is more than 20db, and a deep notch appears at 3.8GHz at the same time.