The Study And Design Of Multi-mode Rectangular Cavity Bandpass Fiters With Controllable Transmission Zeros

With the rapid development of telecommunication in recent years, especially the issuance of 4G license to the three major telecom brands by the Ministry of Industry and Information in 2013, there would be higher demands for telecommunication systems. As an indispensable key component in the whole telecommunication system, filters have a huge impact on not only the quality of communication, but also the whole volume and coat of systems, so studying filters has a great theoretical significance and potential commercial value for the development of telecommunication. Cavity filters, one of the oldest and most vibrant filters in history, have been widely applied in digital television broadcast, satellite communication and base stations, via its advantages of high power handling, low insertion loss, the high quality factor and so on. In this paper, focusing on the rectangular cavity filter, the principal research and innovation lie in following aspects:Ⅰ.A variety of multi-mode bandpass filters were designed and the characteristic of the filters is that there is a pair of transmission zeros which could be controlled independently, which means that the two transmission zeros could be arbitrarily placed on either the left or right side of the passband, enhancing the practicality of the filters designed. In the process, why different modes could be excited is interpreted in detail, which may do an assistance to the design and understand of cavity filters.Ⅱ.A variety of multi-band bandpass filters were designed, including dual- and triple-band bandpass filters. The filters show good performance with quite simple structure and if they could be applied in the communication system, there would help reduce the volume of the system.Ⅲ.Combing the multi-mode and multi-band bandpass filters, a triple-mode bandpass filter and a triple-band bandpass filter are also designed with the help of a U-shaped slot, further validating the theory of above designs.Ⅳ.On the base of the above study, some potential further research directions are analyzed to expand the study and enrich the applications of cavity filters.It is noteworthy that unlike the traditional cavity filters, all the rectangular cavity filters in this paper are designed without any inside coupling tuning elements, such as screws and corner cutting. In this way, it does not damage the integrity of the whole geometrical structure, as well as decreases the cost of fabrication.