Microwave Radiometer Front-End And Its Wide-IF Super-Heterodyne Model And Application

Microwave radiometers act as passive receivers which can receive and detect weak electromagnetic radiation signals emitted by objects.Since the 1960 s,they have been widely used in many fields such as astronomical research,military confrontation,environmental monitoring and so on.In recent years,their function in public security has also aroused the attention of researchers.This thesis focuses on microwave radiometers which are particularly used in imaging systems: designs two Ka-band direct-detection radiometers and analyzes & builds a modeling system concerning wide-IF superheterodyne radiometers,with main contributions as follows.Firstly,to meet the needs of a project,a part of this thesis designs two narrow Kaband radiometers,which separately works with different central frequency.In order to illustrate this work,this thesis comprehensively explains theories regarding whole Kaband radiometer systems and their components at first.Then by analyzing the target of projects,this thesis verifies design principles and hence designes 3GHz bandwidth and 4GHz bandwidth Ka-band direct detection radiometers.The whole process includes the design of two cascaded low-noise amplifiers(LNAs),E-plane fin-line filters,and Kaband detector.With aforementioned designs as miniaturized as possible,this thesis then designs cavities used to hold RF circuits and Printed Circuit Boards(PCBs)which can provide power-supply and latter amplify-RC-amplify function.Final works are individually held in cavities sized as 110mm×19mm×19mm,with temperature sensitivity as high as 0.41 K and 0.42 K at 0.5ms transient time.Secondly,another part of this thesis deducts and builds a novel model of wide-IF super-heterodyne radiometers,which includes the equivalent bandwidth model and the cascaded noise factor model,in compensation for existing radiometer models.The model can be used to calculate wide-IF super-heterodyne radiometer's temperature sensitivity based on characteristics of components,which takes the fluctuation of gains and noises in wide band components into consideration.After the theoretical part,this thesis applies the model and calculates a temperature sensitivity of an unestablished 340 GHz wide-IF super-heterodyne radiometer front-end,in which some IF components are designed by this thesis while a 340 GHz sub-harmonic mixer's simulation results was used.The calculated result shows that this radiometer front-end could achieve temperature sensitivity as high as 0.25 K at 20 ms integrated time.What's more,with the designed IF components,amplify-RC-amplify module,and a bought detector,this thesis establishes a wide-band radiometer that could use matched load to achieve calibration,and tests its temperature sensitivity.The result shows a 0.13 K temperature sensitivity at 1ms integrated time.