Cavity Filters Coupled Structure Theory And Key Technologies

As the information techniques developing rapidly, the microwave communication frequency resource are becoming more and more precious and crowded. It has made a more rigorous technical requirement in the microwave filters design. The key technical requirement is developing the filters with small size, high selectivity, low loss and low cost in a short period of time, which promotes the deeper research in microwave filters.The inductive or capacitive coupling is realized by opening air window or adding probe between resonators in cavity filter. And the narrowband filter will be got by control the strength of coupling inductance or coupling capacitance by changing air window's location, size or probe's thickness, length and so on. Furthermore, it's easily to get the cross-coupling between resonators. And, the location and the number of transmission zero can be achieved by controlling the number and thickness of cross-coupling. The cavity filter will got many advantages as small size, narrow bandwidth, high coefficient of rectangular, high-power capacity when it have a capacitive load. As a result, it have a great application prospects and get a great attention both at home and abroad.Nowadays, the accuracy and efficiency of the electromagnetics analysis software are improved quickly as the fast development of the computer technology and the microwave CAD. Furthermore, the traditional equivalent circuit method and the high frequency simulation technique have been comblined, which will made it easier and fast to design the well performed filters.The purpose of this paper is majored in analyzing the different coupled-structures in cavity filter, especially the influence of the different structures on the performance of filter. The main work in this paper generalized as follow:1. Simplify topological structures. The couple matrix reducing methods for current topological structures is described simply. And the specific reducing processes of coupling matrix in the case of folded type, shaped and wheel-type(CT, CQ) are summarized respectively.2. Calculate the coupling coefficient accurately. The coupling coefficient is calculated accurately when the different coupling structures are used, which include the electric coupling and magnetic coupling. Specially, the electric coupling needs others way to realize or strengthen for it more sensitive.3. Select and design the cavity structure. The entire cavity is draw after step 1 and step 2. Then the simulation software is used to design and optimize its characters.4. Test the filter. Analysis its S parameters, power capacity and VSWR, verify the practicality of the filter. The practicality of the filter is verified by analysis its S parameters, power capacity and VSWR.