Capacitive Load To The Development Of The Filter And Duplexer

With the development of wireless communications, waveguide filters and diplexers with small size, low insertion loss, good frequency-selectivity and farther parasitic bands are needed in a large amount of areas. The purpose of this thesis is to study and design new compact waveguide filters and diplexers with these characteristics. The main works are summarized as follows:Systematic filter design theories are reviewed and formulae for capacity-loaded transmission lines are derived out. A microwave cavity is proposed to realize maximum capacity-loading and minimize the sizes of various waveguide filters. An optimal capacitive loading method is used to design a compact direct coupling cavity filter, the total length reduces by 36%, and better frequency selection performance, compared to the same level direct coupled resonator filter. The concept of capacity-loading is then used in multi-mode filters. A compact capacitive loading multi-mode filter is given, and it achieves excellent performance and small size decreased by 78 percent compared with conventional multi-mode filter. We can see that the capacitive loading technology is widely used in a variety of cavity structures to achieve miniaturized cavity filter.Capacity-loaded waveguide filters are used to construct a compact diplexer. In this paper, a designed diplexer shows that the length reduces above 50% compared to the length of the direct coupling cavity diplexer.For the processing and debugging problems, error correction technique is used in the design of sample devices. This article practice proves that this method has received good effect on the aspects of improving the adjustable filter and product yield.