Study Of The Filtering Properties Of Bandpass Filters With Combinatorial Non-periodic Defected Ground Structure

Photonic Bandgap (PBG) structure is first used in optics region. Several years later, it is extended to microwave and millimeterwave regions, and is called Electromagnetic Bandgap (EBG) structures. EBG structure is capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic allows wide application in restraining the surface radiation of antenna, enhancing the output power of amplifier and oscillator, constructing high impedance microstripe, reducing the size of circuit etc.Combinatorial Nonperiodic Defected Ground Structure (CNPDGS) is development from EBG structure. It is constructed with only one defected unit, and the central frequency of the bandgap which is produced by CNPDGS is holy decided by the size of CNPDGS. Compared with EBG structure, CNPDGS is smaller in dimension and easier to analyze. In one word, CNPDGS is more suitable for integrated circuits.Finite-Difference Time-Domain (FDTD) method is a direct time domain method for solving Maxwell equitation. It can be used to determine the amount of the scatter and the radiation of complex or ununiform object. We can get the frequency domain characteristic of the object by using Fourier transform to the result of FDTD analysis.In this paper, the FDTD method is programmed with the blend of C and Matlab languages, which combines the merits of the two languages. With the help of this powerful electromagnetic simulation programme, we optimize the filtering properties of two bandpass filter with CNPDGS, and study the relationship of CNPDGS and transmission properties. Those circuits mentioned above are tested by measurements. The simulation results show agreements with the measurements.