Study On Microwave Multimode Resonant Theory And Its Application In Filter Design

The wireless communication technology is developing, a variety of new technologies are constantly emerging and a variety of communication systems coexist, which brought new challenges to the design of microwave filter: In order to cope with the congestion of the spectrum resources, so that multiple communication modes work simultaneously, multi-band and broadband filters become the inevitable choice. On the other hand, the miniaturization, low loss, low cost, high performance becomes the general requirements of the current communication system, which makes the researchers pursue of superior performance and design novel filters. In recent years, because of its miniaturization, high performance and so on, multi-mode resonators have been widely used in the design of multi-band and broadband filters.In this paper, a systematic study is conducted on the multimode resonant behavior, and a detailed analysis is performed on the mechanism of multi-mode resonant behavior. Based on the above study, asymmetric stub loaded resonator(ASLR) and stepped impedance stub loaded resonator(SISLR) are proposed, detailed analysis of their resonant characteristics and coupling characteristics and their applications in multi-band bandpass filter(BPF) and wideband filter design are described. Finally, the design method of two kinds of duplex is proposed, which is based on multi-mode resonator.The author’s works mainly consists of:1. Systematical study on the mechanism of multi-mode resonant behavior is given, and the unified multi-mode resonance theory is formed. Based on the above study, two types of multi-mode resonator, i.e., ASLR and SISLR are proposed from two aspects of shape and position, and detailed analysis of the resonance characteristics are made.2. Systematical study on the coupling feeder of the filter is proposed. Detailed analysis of three main feeders and the influence on the performance of the filter is described, and the generation mechanism of transmission zeros is also derived. This provides a reliable reference of engineering design filters and multiplexers for the subsequent chapters. At the same time, it also analyzes the additional other forms of the feed coupling.3. Based on asymmetric stub loaded resonator, a variety of multi-band bandpass filters are designed. Detailed analysis of their resonance and coupling characteristics is carried out, and the general steps and methods for designing filters are presented. As a consequence, filter are designed using the asymmetrical short-circuit stub loaded resonator to verify the application method. Finally, the method of stub-to-stub coupling and frequency division suppression is given, and dual-band bandpass filter is designed.4. Four kinds of design methods of multi-band BPF based on the SISLR is proposed, and the resonance and coupling characteristics of the multi-pass BPF are analyzed in detail. The dual-band passband filter is designed by using the characteristics of the SISLR; The tri-band BPF is designed with the method of multi-path coupling. The tri-band BPF is designed using hybrid resonator.5. The design method of two types of multiplexer is presented, which is based on the dual-frequency impedance transformer technique and the method of dual-frequency filter matching network. A feasible design method is proposed, which is applicable to the design of the duplex. These two methods can be extended to the design of the multiplexer.