Research On Filters' Structure And Performance In Wireless Communication Devices

With the rapid development of mobile communications and the high inte-gration of microwave circuits, microwave filter which act as the key elements of communication system, are demanded toward to high performances and s-mall sizes. This paper does much research work on miniaturization and high performance of microwave filters. By using new technologies, such as defect-ed ground structure (DGS), defected microstrip structure (DMS), dual-mode structure, fractal structure, split ring resonator (SRR), and complementary split ring resonator (CSRR), etc., we propose some kinds of novel filters, such as low-pass filters, band-pass filters and band-stop filters. The microstrip filters are studied by finite element method. The fundamental theory of electromag-netic field and the principal theory of finite element method (FEM) are briefly discussed. The dissertation is classified into four parts stated as follows:Firstly, based on analysis of dumbbell-shaped DGS, the complementary rings are proposed. A class of band-pass filters using the complementary rings are designed. We propose First iteration and Second iteration Koch Island frac-tal DGS, square?DGS and circular?DGS. Koch Island fractal DGS, square?DGS and circular?DGS have a flat low pass-band and band-gap charac-teristic. In order to improve the out-of-band suppression of the DGSs lowpass filters, some effective methods are explored such as H open-stub and arrang-ing the unit structure periodically. At the same time, snake DGS is proposed and two band-stop filters are designed based on the snake DGS which have two transmission zeros. Resonant characteristics of all DGSs are discussed in this chapter. The measured results of the low-pass filters show a good agreement with the simulation.Secondly, the stop-band characteristics of three novel DMS and the differ-ence between DMS and DGS are studied. DMS circuits are not only easier to integrate with other circuits, but also more immune than DGS from crosstalk and ground plane interference. Three DMSs are proposed and the resonant characteristics of three band-stop filters are studied by HFSS 10.0. Three band-stop filters are designed based on the DMSs. The stop-band characteristics of the filters are better. The measured results of the low-pass filters show a good agreement with the simulation. Two band-stop filters have two transmission zeros and one bandstop filter has one transmission zero.Thirdly, based on analysis of triangular dual-mode patch filters, the frac-tal structures are applied in designing dual-mode microstrip patch filters. In this chapter, novel fractal-shaped square patch filters and fractal-shaped regular hexagon patch filters are designed. The degenerate-modes can be well exeited, which improves the pass-band characteristics. At the same time, fractal-shaped regular hexagon patch filters have attenuation poles at each side of pass-band, which efficiently improved the frequeney selectivity. Fractal structure also can reduce the resonant frequency of initial filters, which can realize the filter minia-turization.Finally, the split ring resonator(SRR) and complementary split ring res-onator(CSRR) that act as fundamental composite units to make meta-material are discussed. The resonant characteristics of SRR and CSRR are studied by HFSS 10.0. A novel structure based on CSRR is proposed and the structure has two resonant frequencies. Novel band-pass filters using the structure are designed and studied. At the same time, novel band-pass filters using CSRR based are designed. the resonant characteristics of two classes of the band-pass filters are studied by HFSS 10.0. The electric field is fully used to excite the CSRR, which can decreases the resonant frequency and achieved the pass-band performance. Based on the CSRR, two 1-D CSRR band-pass filters are pro-posed, both filters all have wider bandwidth and better out-band suppression.