| Filters play important roles in the wireless communication system for rejecting unneeded harmonics and spurious signals, whose performance and volume are the key to realize high performance and miniaturization. Especially with the condition of limited spectrum resources, high-performance filter is widely used in today’s wireless communication, which is particularly important for multi-mode, multi-frequency equipment. However, the filters still use traditional instead of integrated technology, which hindering the filters becoming miniaturized and better.Waveguide filters and micro-strip filters not only have the advantages of easy design, low cost, small size and ease of integration with other circuits, but can be easily processed through standard PCB technology as well. All of above means that they catch widely attention since their advent. For the key issues to realize miniaturization and high perfon.ance, this dissertation aims to carry on a further research on the new filters with the equivalent circuits and even-odd-mode analysis. Many filters structures are researched from different aspects so that they can meet specific requirement about bandwidth and pass-band. Main achievements are as followed:1. Two dual-band filters are implemented by CSRR-HMSIW structure loaded by the compact short-circuited CRLH-TL structure and CSRR-HMSIW by CSRR-DGS structure, respectively. The corresponding properties of this filter with high performances and miniaturization can be achieved through the combination of CSRR-HMSIW structure and compact short circuited of CRLH-TL structure. Curve-fitting is used to acquire the corresponding relationship between units and equivalent circuits. Then two cascaded units achieve a dual band response, and the center frequencies are 2.5GHz and 5.4GHz, respectively. The tapered-line feeds are applied to realize the mode conversion and impedance match, and to improve the overall performance of the filter.2. A new stepped-impedance resonator (SIR) structures is used to implement dual-band and tri-band filters, respectively. Based on the even-odd-mode theory, the analysis of SIR structure is carried out to extract the relationship between the impedance ratio, electrical length and the fundamental frequency, harmonics, and to design a miniaturized filter. Using skew-symmetrical 0° feeding structure, four transmission zeros are introduced to improve the band rejection. Additionally, the pass-band of the tri-band filter is introduced by the coupling between the source and the load.3. A dual-band filter is implemented by use of the dual-loop SIR structure proposed. The analysis of dual-loop SIR structure is carried out on the basis of the even-odd-mode theory to achieve the relationship between the structural parameters and performance. Besides, four transmission zeros is introduced by the coupling feed and transmission characteristics of the SIR unit to improve the stop-band rejection and the pass-band isolation.4. A wideband filter is designed on the base of the proposed tri-mode SIR structure. The analysis of tri-models SIR resonator structure is carried out on the basis of the even and odd-mode theory and the corresponding properties of the structure also are verified by the FDTD electromagnetic simulation. Then the relationship between the resonant frequency and the structure parameters is extracted and the corresponding resonant frequency of this tri-models SIR resonator is used to implement a broadband filter. The measured filter obtains an insertion loss less than 0.39dB, excellent passband flatness and frequency selectivity. |
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