Researches On Controllable Multi-Band Filters

With the rapid development of communication industry, especially a variety ofcommunication standards proposed, the communication system which can be compatiblewith multiband has become the trend of development. Microwave filter plays an importantrole in a communication system, it largely influences on the overall performance of thesystem. Therefore, microwave filters need to have the characteristics of miniaturization,multi-band, controllability, and high performance in the communication system. Base onthese characteristics, this dissertation focuses on the design method of multi-band bandpassfilter (BPF) with controllability. Some kinds of resonators and coupled structures areproposed and applied in designing multi-band BPFs. The main contributions of thisdissertation can be summarized as follows.Based on the symmetrical stub-loaded resonator (SLR), an asymmetrical stub-loadedresonator is put forward in the dissertation. Analyzed the resonant characteristics of theresonator by transmission line theory, the first two resonant frequencies are completelyindependent. Two dual-band BPFs with independently controllable frequencies andbandwidths are designed by adopting the asymmetrical SLRs.Based on the SLR in-depth study, two kinds of novel multi-stub-loaded resonators areproposed and their resonant characteristics are analyzed. The first three resonant frequenciesof the tri-stub-loaded resonator are fully independent. The tri-band BPF usingtri-stub-loaded resonators has independently controllable features like passband frequenciesand bandwidths. Another kind of multi-stub-loaded resonator is applied in high-orderdual-band BPFs with independently controllable frequencies and bandwidths.One dual-mode resonator and its application to dual-band BPF with wide stopband arepresented. The size of the filter is very small, which can be easily integrated in PCB.All of the proposed filters are simulated, fabricated and measured. The simulated andmeasured results are in good agreement, which verify the design methods.