Design Of Microwave Lossy Filter

With the rapid development of wireless communications, the microwave / millimeter-wave systems are widely used and the spectrum congestion is becoming more and more prominent. In order to make more efficient use of limited spectrum resources and make the communication systems miniaturization, lossy filters could deal with the issues of high-performance and weigth at the same time, and researchers have paid more and more attention on the lossy filter.This thesis mainly focuses on the design of microwave lossy bandpass filter. The lossy filter is proposed for the improvement of weight and size of the high-performance filter. Microwave lossy filters have been studied during the recent years, and certain achievements on the lossy filters were obtained, such as the lossy filter synthesis theory. But, there are still a lot of work on the lossy filter design and implementation can be carried out on. This paper has more concern on the design of lossy filter and their physical implementation. The major work is concluded as follows:Firstly, the traditional lossless filter synthesis theory is introduced as the basic theory, and details analysis of lossy filter synthesis process is presented. after that, the simplification of lossy filter coupling matrix is analyzed, meanwhile, the key technologies on microwave lossy filter are introduced.And then, study of nonuniform Q lossy filter is carried out. The unloaded Q-factor of substrate integrated waveguide resonators and microstrip resonators are investigated. Based on the study, a microwave lossy filter based on a hybrid of SIW and microstrip technology is designed. The improvement of insertion loss under nonuniform Q lossy filter is presented, and the proposed lossy filter was fabricated and measured. Good agreement between the simulated and experimental results can be observed.Finally, microstrip lossy filter with resistive coupling is investigated.The impact of resistive coupling over the filter performance is considered when design a lossy filter and analysis of the implementation of resistive coupling is carried out. Based on the research above, a fourth-order microstrip lossy filter is designed. The proposed lossy filter was fabricated and measured, and the measured results validates the design concept.