Research On Tunable Filter Of Evanescent Mode Cavity Based On Photosensitive Glass

With the rapid development of wireless communication technology,the reliability requirements of which also increases.Tunable filter can solve the noise interference problem in a wider range of frequency band,which has become one of the research focuses of the current filter.Although the commonly used tunable filters’ performance has been improved,there still exists defects.Evanescent mode cavity tunable filter has important research value because of its high quality factor,wide frequency adjustment range,low volume and power consumption.In this paper,the theoretical principle of the evanescent mode filter is introduced.Besides,the evanescent mode filter is simulated and analyzed by HFSS.Based on these results,the evanescent mode filter based on photosensitive glass is made,tested and analyzed.The main experimental results are as follows:1.Starting from the theoretical derivation,the working principle of the evanescent mode resonator is introduced and,the resonance frequency together with the inherent quality factor are calculated.At the same time,the correctness of the theoretical formula is verified by the three-dimensional electromagnetic simulation software HFSS.2.The influence of resonator size on resonant frequency and inherent quality factor is analyzed by HFSS software.The results show that the resonant frequency decreases with the increase of the radius of the cavity,the radius of the capacitance column,the height of the cavity and the decrease of the distance between the capacitance column and the cavity.At the same time,only when the radius of the capacitor column increases,the intrinsic quality factor decreases.In addition,the input-output coupling model of resonator port and the coupling model between resonators are simulated and analyzed,and the coupling parameters are adjusted.Then full wave simulation is carried out to adjust the return loss,insertion loss and other indicators to meet the design index.Finally,when the cavity radius R is 6.6 mm,the column radius R is 1 mm,the column height h is 8 mm,and the spacing D increases from 20 μm to 50 μm,the center frequency increases from 2.21 GHz to 3.02 GHz.3.Guided by the size parameters obtained from the simulation,the self-made photosensitive glass is used to process the filter through exposure,annealing,etching,magnetron sputtering and other processes.The results show that when the voltage increases from 0 V to 93 V,the center frequency of the filter increases from 2.16 GHz to3.43 GHz;the return loss decreases from 16.14 dB to 8.17 dB;the insertion loss increases from 1.87 dB to 5.22 dB;and the 3 dB bandwidth increases from 38 MHz to50 MHz.