Study Of The Bandgap Characteristic Of Combinatorial Non-periodic Defected Ground Structure For Coupling Microstrip Filter

Electromagnetic Band gap (EBG) are periodic structures capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic of EBG allows wide application in high-Q, low-pass filters, power dividers and so on. The Combinatorial Non-periodic Defected Ground Structure (CNPDGS) is developed at the base of EBG. It is capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies like EBG. The structure of CNPDGS is entirely different from the structure of periodic PBG. Compared with periodic PBG, the structure of the CNPDGS is simpler in structure, smaller in dimension and lower in insertion loss.The low pass filter and band pass filter with structures of CNPDGS are calculated with finite-difference time-domain (FDTD) method in this paper, through which we will obtain the electromagnetic waves of time-domain propagated in the FDTD domain. Then the frequency characteristic of the structures can be computed by Fourier transform. The FDTD method is programmed with the blend of C++ and Matlab languages,which can be used to calculate Low pass filter and Band pass filer formed by coupling microstrip. Nonuniform mesh method is studied in this paper. Some conclusion about the errors bringing by nonunifrom mesh method is got, and it is explained and proved by examples.At last, a new band pass filter, which provides a wide band (3GHz to 4GHz), is proposed on the base of two kinds of filter talked in this paper. It will have a wide application in communication.