Research On Novel Planar Dual-mode And Multimode Bandpass Filter

With the development of wireless communication technology, communication devicesbecome smaller and smaller, which put forward a very high standard and requirement on themicrowave filters. The study mainly focus on the performance improvement and sizereduction of the microwave filter. Dual-mode and multimode resonators are one of the mosteffective means to the miniaturization of the microwave bandpass filter, because of theirsingle resonators can be equivalent to the multiple resonators. This thesis gives acomprehensive study on the design of novel planar dual-mode and multi-mode filters. Themain contribution of the thesis include the following aspects:Firstly, a novel dual-mode bandpass filter based on defected ground waveguide (DGW)is proposed. The filter consists of a stub-loaded dual-mode DGW resonator. By tuning thelength of the loaded T-shaped stub, dual-mode characteristics is obtained and the bandwidthalso can be changed. To further decreasing the size of the filter, the DGW resonator is foldedin spiral shape. The filter is designed and fabricated. Measured results verifies the proposedtheory.Secondly, a fractal hexagonal dual-mode bandpass filter is designed. A T-shapedspur-line is loaded to the resonator to achieve dual-mode characteristics. In-line feeding isused to achieve the desired external coupling. The filter is compact since the fractal techniqueis used, which decreasing the circuit size greatly.Finally, a novel hybrid triple-mode SIW filter is analyzed. Triple mode are achieve inone filter, including the resonant mode of the SIW cavity and the modes that are excited bythe loaded dual-mode resonator. Without increasing the size of the filter, additionaldual-mode is obtained easily and hybrid multi-mode bandpass filter is realized. It introduces anew way for realization of multi-mode filter.