Microwave Filter Design Using Fragment-Type Structure

Filters are important components of wireless communication systems, the methods to realizing their miniaturization and high performance are constantly pursuing goals of the researchers. Different from regular structures, this dissertation proposes and explores an irregular structure, named Fragment-type structure, for filter design. By using multi-objective evolutionary algorithm based on decomposition combined with enhanced genetic operators (MOEA/D-GO), several design examples are given. The main work in this dissertation can be summarized as follows:Firstly, a fragment-loaded resonator structure is proposed, and two filters are designed. For resonator, with its internal empty area filled with fragment cells, the area of current and charge distributions is increased, which can realize miniaturization, and the periodic distribution of resonant frequencies is broken by the irregularity of the Fragment-type structure, providing a chance to adjust the frequency distance between the minimum spurious resonant frequency and the fundamental resonant frequency, which helps to realize good parasitic passband suppression in filter design. Because of the appearance of transmission zeros, the designed filter has good frequency selectivity. In addition, the position of the transmission zeros can be adjusted by adding a source/load coupling line, which can improve the steepness of transition band.Secondly, the application of Fragment-type structure in stub-tapped filter design is explored. A Fragment-type loading structure is proposed to replace stub-tapped lines, and three filters are designed. Analysis shows that the structure can generate one transmission zero near the passband, and the position of the transmission zero can be controlled according to the requirements of stopband suppression.Thirdly, choose a3-order parallel-coupled filter as a reference, coupling line structure near the input and output ends of the3-order parallel-coupled filter is replaced by Fragment-type structure, intuitively shows that with the same size, the Fragment-type structure can improve the filter performance; and with similar performance, the Fragment-type structure can miniaturize the filter.Finally, Fragment-type structure is applied in MIMO antenna isolation resonator design to expand its scope of application. By filling fragment cells into an existing resonator which has metamaterial property, an isolation resonator is proposed. The designed Fragment-type isolation resonator also has the metamaterial property, and good isolation and large isolation bandwidth are achieved when placed in the MIMO antenna which is composed of two monopoles. Besides, the presence of the isolation resonator does not affect the essentially omnidirectional nature of the radiation patterns, with the total gain being practically unaffected.