Design And Fabrication Of Tunable Evanescent Mode Resonator

The tunable filter as a key element in the radio frequency front-end is mainly used to suppress the frequency band which is out of the radio frequency signal,select frequency and reduce the cross-modulation distortion of the receiver.The performance of the tunable filter directly determines the performance of the wireless transceiver system.Therefore,the high performance tunable filter with a wide tuning range,high quality factor,low insertion loss,high linearity,integration and low cost is the urgent demand by the next generation software radio and wireless communication system.This article takes the new evanescent mode cavity technology tunable filter as the research object,using HFSS(three-dimensional electromagnetic simulation software)to analyze the influence factor of quality factor and the frequency tuning range.Finally,we can obtain the parameters with the highest tuning rate by optimizing.The MEMS(MicroElectro-Mechanical System)process is used to experiment on the photosensitive glass,and finally the wide adjustable evanescent mode resonator with full glass structure is fabricated and tested.The main results of this paper are as follows:First,Using HFSS to analyze the electric field and magnetic field of a rectangular cavity and the vanishing mode resonator,which can be concluded that the resonator has the characteristics of miniaturization and high quality factor(Q value).By simulating the coupling mode of coaxial line and resonator,which can be found that the coupling strength is proportional to the distance between the probe and the capacitance column.Second,it is analyzed the influence of evanescent cavity size on resonator resonant frequency and Q value from theory to simulation,and the main methods for increasing the tuning rate are as follows:(a)Reducing the physical dimension of the resonant cavity and capacitance column.(b)Reducing the distance between the two polar plates of loading capacitor.(c)Adding the high dielectric constant and low loss dielectric film between loaded capacitor plates.At last it is optimized the size of each part with higher tuning rate by HFSS,the radius of the cavity is 3mm,the height and radius of the capacitor column are 1.6mm and 0.22 mm respectively,and the dielectric film is added between the two plates of loaded capacitor.Through the simulation of evanescent mode resonator,it is found that the tuning rate reaches above quadrupling frequency.Third,based on the simulation model and the principle of MEMS processing,it is explored the experiment of making the wide adjustable evanescent mode resonator on the photosensitive glass.Finally,the evanescent mode resonator with a full glass structure was successfully machined and passed through a vector network analyzer.The test shows that the tuning range is 1.8GHz-8GHz,and the tuning rate is close to quadrupling frequency.