| Microwave remote sensing technology plays an increasingly important role in Earth observation,atmospheric detection,weather monitoring meteorological disaster warning and etc.At present,Chinese meteorological satellites mainly include polar orbit meteorological satellites and geostationary meteorological satellites.Constrained by the operating mode of polar orbit meteorological satellites,the temporal resolution is low.Due to the high orbit altitude of geostationary meteorological satellites,the spatial resolution of microwave radiometer is relatively low.The large aperture antenna is required to achieve spatial resolution on an order of several tens of kilometers,which brings great challenges for mechanical manufacturing and in-orbit scanning.The microsatellites constellation is an effective means of taking into account both temporal resolution and spatial resolution.This dissertation is based on the method of microsatellites constellation for microwave radiometers observing the Earth with purpose to achiev a temporal resolution of 30 minutes and a spatial resolution of 15 kilometers.The researched three key technologies which include microwave radiometer miniaturization system designing,RF front-end terahertz frequency separation technology and antenna scanning drive-servo system based on active disturbance rejection control.Theoretical analysis,system design and simulated and experimental verification have been carried out for three key technologies.The main research contents are as follows:(1)A miniaturized microwave radiometer system scheme for the microsatellite platform has been proposed.Operating frequency channel selection,index demonstration and top-level design of the microwave radiometer have been researched.The frequency separation scheme of RF front-end,the Earth imaging observation geometry and the antenna scanning mode have been analyzed in detail.The microwave radiometer includes four detection frequencies at: 89GHz(with one channel at window band),118GHz(with five channels at oxygen absorption peak),166GHz(with one channel at window band)and 183GHz(with three channels at water vapor absorption peak).The four frequencies use the technology of multi-frequency band sharing one feed and one offset parabolic antenna.The receivers of the window frequencies adopt direct detection type,and other frequencies for the receivers are superheterodyne mixing types.Polarization separator and waveguide diplexer are used to realize the frequency separation of RF system.This design scheme has more advantages in volume,weight and power consumption than the existed microwave radiometer on FY-3 series satellites and it is more suitable for the microsatellite platform.(2)Research on the frequency separation technology of the terahertz frequency has been carried out.The 89/118 GHz and 166/183 GHz diplexer are designed by using network synthesis method and mode matching method,and it is the first time in China to design,process and test the waveguide diplexer in this frequency band.Two waveguide diplexer models have been simulated and verified by using HFSS software.From the perspective of maching,the analyses of 166/183 GHz diplexer surface material,inductive iris thickness,inductive iris steepness and dimensional sensitivity have been carried out before their manufacture.From the perspective of measurement,two diplexers are measured using a vector network analyzer and frequency expansion modules.From measurements,the maximum insertion loss is 1.5dB and minimum return loss is 15 dB,and out-band rejection is higher than 25 dB.Good agreement between simulation and measurement has validated the feasibility of the diplexer designing method.(3)Multi-mode scanning control algorithm of servo system for microwave radiometer antenna scanning mechanism has been researched.The implementation scheme of introducing the second-order speed active disturbance rejection controller into the scanning control is proposed,which improves the robustness of the servo system.The PI(Proportional-Integral,PI)controllers of current loop,speed loop and position loop are designed by analyzing vector control strategy and the d-q axis mathematical model of permanent magnet synchronous motor.Three scanning modes,namely constant speed scanning,variable speed scanning and fixed point observation,have been simulated and tested.According to the simulated results,no overshoot and no static error control are realized for the fixed point observation mode.For the constant speed and variable speed mode,the transition time is shorter and the overshoot is smaller.However,when the system is suddenly disturbed,the speed changes greatly and which demands a long time for restoring to the original state.Due to the poor anti-interference ability of PI controller,this dissertation introduces the second-order speed active disturbance rejection controller into the modes of constant speed and variable speed.Comparisons of response characteristics of the second-order speed active disturbance rejection controller,second-order speed linear active disturbance rejection controller and PI controller have been carried out and the results show that the system of second-order speed active disturbance rejection controlling has smallest overshoot and shortest recovery time when the system is suddenly disturbed.Therefore the control system is robuster and more disturbance-resisting.(4)The hardware platform of drive-servo system for the antenna scanning has been built,and the software design of permanent magnet synchronous motor control algorithm and signal interface modules have been completed.The response characteristics of the second-order speed active disturbance rejection controller and PI controller in constant speed and variable speed mode have been compared experimentally.Second-order speed active disturbance rejection controller has good control performances in terms of step response characteristics,variable speed response characteristics,steady-state performance,disturbance-resisting performance and etc.The control accuracy of constant speed mode is 1.78%,and the control accuracy of variable speed mode(Earth observation phase)is 3.5%.Scanning period errors of both scanning modes are not more than 1ms.Positioning accuracy of fixed point observation mode is about 0.00206o.Generally,all three scanning modes behave good dynamic and static characteristics,as well as high control accuracy. |
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