Reseach And Application On Design Technique Of Ultra-wideband Resonator

Resonator, a microwave passive device featuring frequency selection and energy storage, is widely used in the microwave measurement and the design of certain components such as filters, oscillators and cymometers. However, the only mode the resonator usually operates in is of a narrow bandwidth, which inevitably makes the wideband test on the resonator complex and costly as several cavities are needed for the test. Therefore, it is of great significance to realize the ultra-wideband test on the resonator with one cavity covering the whole bandwidth.Based on the analysis of the common transmission line resonators’ advantages and disadvantages, the research purpose of using one cavity to cover the 1~40GHz ultra-wideband is achieved by innovatively designing the 1~40GHz resonator cavity with two structures—the coaxial cavity in 1~7GHz and the TE0 np cylindrical cavity in 7~40GHz and integrating them into one cavity.This article focuses on the design of the 7~40GHz cylindrical cavity, which involves: firstly, to figure out the range of the cylindrical cavity’s size according to the resonant frequency formula of the TE0 np mode; secondly, to build the model by adopting the mode purification principle and the rear-cavity processing technology and to optimize the size of the stepped gap piston with the HFSS software; thirdly, to complete the design of the integrated resonator after analyzing the coupling type and coupling location. In the design of this paper, all the following issues are taken into thorough consideration:1.The suppression of the interference modes:In the paper, there are altogether three steps in suppressing an enormous amount of interference modes around the working mode: firstly, to optimize the length of the cylindrical cavity by following the mode purification principle; secondly, to suppress the interference modes which contain vertical current components by following the rear-cavity processing technology and using the stepped gap piston; finally, to suppress the degenerate mode with the double-ridge waveguide / rectangular waveguide excitation;2.The design of the coupling structure:The7~40GHz cylindrical cavity features in the aperture-coupled excitation. It is a must that the coupled port should be opened at the maximum field strength of the working mode, and meanwhile, the opening must minimize the influence left on the design of the 1~7GHz coaxial cavity. Then, the coupled port of 7~26.5GHz should be located at the side wall while the coupled port of Ka band should be located at the upper end cover; and meanwhile, the 1~7GHz coaxial cavity ought to be coupled with a probe.3.The design of the integrated cavity structure:This is realized by calculating the diameter of the adjusted coaxial inner conductor to get the 0Q value of the coaxial cavity reach its maximum, taking into account the interaction between the two cavities, optimizing the coupling structure, and completing the design of coaxial cavity.According to the complex permittivity testing principles of the cylindrical cavity and the coaxial cavity, the research ends with setting up a resonator testing system which can work at 1-40 GHz, measuring the sample with the perturbation method, and making an standard error analysis of the test result. Over the entire frequency band, the test standard error is ?? ?? ? ?1% and5 tan ?12% tan ?6 10?? ? ? ?. The test result shows that this research is of a reasonable design and meets the expectation.