Study On Transmission Property Of DGS Microwave Filter With Different Structures

Defected ground structure (DGS) is a novel microwave circuit and it is originallydeveloped from photonic band gap structure (PBG). Some given forms are artificiallyetched on the metallic ground plane of microwave circuit in order to make the currentdistribution of ground plane change. Thus it can affect transmission lines' frequencyproperty and prohibit the electromagnetic waves propagating within the certain rangeof frequencies. DGS can obtain high-performance of microwave circuit, and can bewidely applied in the field of high-Q cavities, low-pass filters and so on. DGS canreduce coupling between systems, suppress side lobe of antenna radiation so as toincrease the gain and bandwidth.The main contributions of this paper are given as follows bythe author:1. The accurate transmission coefficient of DGS is detailedly obtained throughfinite-difference time-domain (FDTD) numerical analysis. Perfectly matched layer(PML) can be utilized to absorb electromagnetic waves in FDTD, and the influencesof PML layer number on analyzing the frequency property are intensively studied inthis paper. The influences of different dielectric and different array distribution on thefrequency property are also calculated in detail. Anovel nested double U-shaped DGSis proposed based on analyzing the frequency property of basic DGS, which hasexcellent double stopband characteristic with the first sharp stopband. Anovel tunablerectangular ring DGS is presented, which has excellent band-stop characteristic. Theinfluences of straight microstrip line on the frequency property are thoroughly studied,which is appended on the microstrip plane. The influences of structure dimensionsand cascaded cells on the frequency property are also studied. Anovel open dumbbellDGS is presented in this paper, which can be developed to design the low-pass filter(LPF) with excellent low-pass characteristic. A novel rectangle rings with evolvingedge DGS, which is proposed in this paper, has sharp cut-off low-passcharacteristic.The frequency property is studied in depth and some control methods offrequencypropertyare obtained.2. Alternating direction implicit FDTD (ADI-FDTD) and Crank-Nicolsondifference FDTD (CN-FDTD) are chosen to calculate the frequency property of DGSin order to save computation time.3. Artificial neural networks (ANNs) and data fitting technique are combined withFDTD to analyze DGS. The computation results demonstrate that the trained ANNs can quickly provide precise answers to the task they have learned and it can greatlyovercome the disadvantage of FDTD in consuming computation time. DGS isanalyzed by parallel FDTD based on domain segmentation scheme. Parallel FDTDand serial FDTD computation results match each other quite well. It is shown that themethod is a powerful approach for the fast analysis and precise design of DGS.4. The experimental microwave circuits of some DGS are designed andmanufactured in Hebei Semiconductor Research Institute at last, and the measuredresults show good agreement with FDTD results, HFSS results and the results ofmeasurement in the references. It is shown that FDTD programs in this paper are veryprecise and effective, which are programmed by integrating the C++ and Matlablanguages and have both the merits of two languages.