Filter Technology Research Based On Defected Ground Structure

The defected ground structure(DGS)is based on the photonic bandgap structure(PBG).By etching periodic or non-periodic defect cell structures on the metal ground plane of a planar microwave device,the defective ground structure is formed.DGS can change the distribution parameters of planar microwave devices such as distributed capacitance and distributed inductance by changing the current distribution characteristics on the metal ground plane of a planar microwave device.At the same time,DGS has the characteristics of slow-wave,stop-band,and high transmission line impedance.These characteristics have great advantages in improving filter performance.DGS has a simple structure,that is easy to integrate and process,and can effectively reduce the size of microwave circuits.At the same time,its design method and equivalent circuit analysis are relatively simple.Therefore,it has been deeply studied by scholars and has accumulated many research results and experiences.This article is based on the study of the basic theory and design methods of DGS.The main work and innovations are as follows:1.By using the advantage of Koch fractals and combining the characteristics of slow-wave effects of DGS,this paper improves the traditional asymmetric DGS structure and constructs a the Koch fractal DGS of low-pass microstrip filter with a stopband bandwidth of 2.2 GHz-12 GHz.2.The filter's stopband bandwidth and stopband attenuation characteristics are greatly improved by means of Kaiser's cone-shaped Koch fractal DGS combined with modified K = 0.9 taper distribution of the microstrip width.3.Through the analysis and comparison of cables with different filtering characteristics formed by different DGS transplanted way,then design a Multi-pass low-pass coaxial filter based on the way of spur-line DGS(S-LDGS)and electrical connection of the core wire.