Design And Implementayion Of Atmospheric Waveguide Measurement System

The influence of atmospheric medium on electromagnetic wave will produce the phenomena of reflection,refraction,scattering and absorption.The atmospheric duct will be formed under the trapped refraction.In this environment,the loss of electromagnetic wave is small,which can overcome the influence of earth curvature and realize beyond-the-horizon detection and transmission.Atmospheric duct environment will influence the detection performance of radar.On the one hand,atmospheric duct can realize beyond-thehorizon detection transmission,on the other hand,we can make up for the electromagnetic shadow zone under the atmospheric duct.Make fall use of the atmospheric duct is one of the hot issues in the field of radar research.The first problem is accurately measure the atmospheric duct.By measuring the atmospheric refractive index gradient,it can be used to determine whether the conditions of the atmospheric waveguide are satisfied.Online measurement can not meet due to the poor measurement accuracy of radiosonde,meteorological instrument and prediction model,the delay in information transmission and processing.In this article,microwave refractometer is developed to online measure the atmospheric waveguide accurately.Based on the principle of PLL and resonant cavity perturbation,the refractive index is measured by the relationship between the resonant frequency of the cavity and the dielectric constant.In this article,introduce the characteristics of atmospheric duct environment and some measurement and inversion methods.The advantages of microwave refractometer are explained through comparing with other measurement methods.Analyze the principle of instrument and signal process,presente the technical index of microwave device and circuit unit of microwave refractometer.The microwave unit is composed of waveguide coaxial changer,attenuator,circulator,tuner and resonant cavity.After assembly and debugging,correcte the cavity resonant frequency error by using a regulating rod under normal temperature and atmosphere.Because of the size of the source carrier frequency and cavity frequency affect the amplitudephase relationship between the standard signal and detector output signal.Based on this design of the whole circuit,it function as a PLL.It is composed of VCO,frequency multiplier,IF amplifier,phase detector,integrator,IF modulation crystal oscillator.When the loop is locked,the VCO output signal through frequency mixing with the standard unit signal,after filtering,the output signal with refractive index information.After connection and debugging,through practical test,measured the gradient of refractive index at a certain horizontal height.After practical testing,it is proved that the microwave refractometer can realize the measurement work under different climate environment,and has the advantages of high stability,fast speed and good continuity,which can realize the high precision real-time measurement of atmospheric duct.