Research On Compact Filter With Mixed Coupling Of Multilayer

As a freqency selection device, filter plays an important role in the RF and microwave communication systems, while the integrated development of microwave communication systems puts a higher demand to filter miniaturization. Filter integration and miniaturization becomes one of the hottest research in this field.First of all, the paper introduces the application background and the research status at home and abroad, put forward the significance of the research and the research contents of this paper. Based on explaining and demonstrating mathematical model of general Chebyshev and coupling matrix synthesis theory, frequency-dependent coupling matrix is formed by introducing the frequency-dependent coupling amount to traditional cross-coupling matrix. It laid the theoretical foundation for the study of new filter circuits later.Secondly, the paper proposes a closed-loop structure stepped impedance resonator(SIR) structure, which uses closed stepped impedance transmission line resonator instead of the traditional low-impedance transmission line. SIR resonator, high impedance line and other resonant structures can be embedded into the closed-loop, which produce mixed coupling between resonators and reduce filter size. Based on the ring SIR resonant structure, 2nd-order, 3rd-order mixed coupling filters and 4th-order cartridge type filter were carried out research and analysis. These filters have a more compact size and out-band transmission zero controllable. Meanwhile, the paper proposes a load open circuit SIR resonance unit, which can control the harmonic frequency of the SIR resonator more flexible. With this unit, a series of single-layer and multi-layer dual-band bandpass filter is designed. By introducing multiple transmission zero near the passband, these dual-band filters improved frequency selectivity.Then, the paper applied electromagnetic mixed coupling to filters which have substrate integrated waveguide(SIW) structures. A multi-layer hexagonal cavity SIW filter and a dual-mode hexagonal cavity SIW filter were researched. To determine the structure and implementation of mode excitation within the cavity, the electric and magnetic field distributions of hexagonal SIW cavity were analyzed. Beaucause it has advantage of flexibility, single cavity dual-mode SIW filters with different transmission characteristics were implemented. Additionally, for smaller size, based on its multi-mode characteristics, we introduced mixed coupling to the source/load(S/L) coupling paths by arranging arched gap between the resonator structure from top to bottom, that achieved a dual-mode cavity hexagonal SIW filter with multi-layer structure.Finally, the paper describes mixed coupling filter in antenna, which combines electromagnetic mixed coupling filter and anttenna together to form a filtering anttenna. In this paper, an end launch filtering anttenna based on broadband filtering balun is studied, and the odd-even mode impedance characteristics of it is analyzed. This filtering antenna features wide bandwidth, high selectivity, compact structure, high radiation efficiency, etc.