Research And Design Of The Sir Structure Duplexer

With the development of modern microwave technology, the communication systems demand high-performance channel, especially miniaturization and high performance of microwave filters and duplexers. Duplexer, as an important component of the communication system, it’s performance directly impact the performance of the entire communication system. Therefore, it’s very important to study the duplexers which have high-performance, small size and short development cycle.The stepped impedance resonator (SIR) structure is detailed studied firstly. A new method which depended on the resonant frequency and unloaded Q to accurate compute the physical parameters of the SIR coaxial cavity is proposed and the detailed design process is given in this dissertation. A band-pass filter of the SIR structure is designed, showing the features that the parasitic pass-band is far away.Then I focus on the band-stop filters. When we have to suppress the interference signal which has a very narrow bandwidth in some communication systems, a band-stop filter with a very narrow stop-band will be useful to solve the problem. But the traditional band-stop filter is difficult to achieve very narrow stop-band, because the traditional structure of band-stop filter is hard to achieve very small coupling. A side-coupled band-stop filter with a very narrow stop-band has a good performance, the relative bandwidth of the stop-band is less than1%and the suppression is more than40dB, is proposed in this dissertation. Wide pass-band band-stop filters are widely used in communication field, because it can provide a very wide pass-band. A wide pass-band band-stop filter which is proposed by Ralph levy has been improved in this dissertation, the designers enable to control the range of the pass-band, which can increase the design precision and flexibility of such a improved band-stop filter.The volume of the traditional band-stop filter is very big, when it is applicated in the low-band of the microwave, because of the limit of the theoretically quarter wavelength. On the basis of researching and analyzing several latest miniaturized band-stop filters, a new type band-stop filter which use the SIR technology and the capacitive loaded transmission line is designed. The advantage of the filter is the size on horizontal and vertical of the filter can be reduced, and process easily. It have a good pass-band performance, and the suppression is more than70dB. The volume of the band-top filter is25%-50%less than the traditional cavity band-stop filter, showing very superior performance in miniaturization.Finally, the SIR structure and the capacitive loaded transmission line which is present in this dissertation are used to design a duplexer in which one channel is band-pass filter,the another channel is band-stop filter, the design ideas and the design process is described in detailed. The structure of the public port is designed independence in order to simplify the difficulty of such a duplexer design.