Design And Experimental Study Of Single-Port Ventilated Microwave Resonant Cavity

With the improvement of radar system,in order to improve the detection accuracy of radar,the electromagnetic wave transmission medium is studied.Atmospheric waveguides are found to occur on the Earth's surface,especially evaporative waveguides at sea with high probability.Atmospheric waveguides are similar to metal waveguides in which electromagnetic waves are reflected forward,changing the original ray trajectory.Not only that,but particles such as gas molecules in the air can also cause attenuation of electromagnetic waves.Eventually,the radar miscalculates the target's position,speed and other information.Above all,there is urgent to know the information of atmospheric parameters in order to predict the electromagnetic wave propagation trajectory and thus improve the radar detection accuracy.Compared with capacitive refractometers and meteorological instruments for measuring gas parameters,microwave refractometers based on the relationship between the resonant frequency of a resonant cavity and the dielectric constant can achieve high-precision measurement of gas refractive index.With a microwave resonant cavity as the main measurement sensor,the microwave refractometer has higher measurement accuracy and stronger anti-interference capability,making it one of the high-precision devices for real-time measurement of gas refractive index.In order to further improve the measurement accuracy of the microwave refractometer,it is necessary to optimize the design of the main measurement element,the single-port ventilated microwave resonant cavity.In this paper,firstly,according to the working environment of microwave refractometer and the system requirements,the corresponding design indexes are proposed for the adapted single-port resonant cavity with vents.The overall dimensions of the resonant cavity are designed according to the waveguide and resonant cavity theory.The TE011 oscillation mode is selected because of a high quality factor.Energy transfer by hole coupling with rectangular waveguide excitation.Considering the need to ensure air ventilation requirements and avoid electromagnetic leakage as much as possible,curved vents were designed.After the theoretical design,the dimensions of the resonant cavity,coupling holes and vents were designed and optimized using ANSYS Electronics Desktop software.An adjustable telescopic rod is installed at the center of the end cover of the cavity to adjust the resonant frequency.Indium steel was chosen as the processing material for the resonant cavity to reduce the cavity deformation due to temperature change.The cavity is silver-plated to avoid the frequency bias caused by the skin effect.Finally,the performance of the machined resonant cavity is measured using a vector network analyzer.The resonant frequency and unloaded quality factor calculation methods given in this paper are used to calculate.The experimental data prove that the single-port resonant cavity with vents designed in this paper has good frequency selection characteristics.The resonant cavity is well matched with the post-stage system,achieving the expected design specifications.