Wide Intermediate Frequency Radiometer Research And Its Terahertz Frequency Application

Microwave radiometers act as passive receivers which receive and detect weak electromagnetic radiation signals emitted by objects.Target recognition is realized by distinguishing the electromagnetic radiation power signals of different objects.Since the1960s,radiometers have been widely used in many remote sensing fields such as astronomy,military,environment,public security,and so on.With its non-metal penetrating ability,terahertz radiometers are used in security inspection to detect hidden metal target.This thesis systematically introduces the theory of radiometers,and develops modules applied to passive imaging:two sets of ultra-wide-band microwave radiometers and a F-band low noise amplifier.The microwave radiometers work as the IF circuits of THz super-heterodyne radiometers.And a THz radiometer is used in a passive imaging system to realize high-speed imaging and metal target detecting.Firstly,this thesis designs two wide-band radiometers,which separately work during2.75～20GHz and 3～22 GHz.In order to illustrate this work,this thesis comprehensively explains theories regarding whole radiometer systems and their components at first.With the theories explained,the indicators of radiometers could be assigned to each unit circuit.An ultra-broadband detector is designed for the radiometers,and its voltage sensitivity in3～22GHz is greater than 1600m V/m W.The PCB of the power supply circuit and the radiometer cavity are designed.The volume of the radiometer is 58×19×15mm~3.The temperature sensitivity of the 3～22GHz direct-detection microwave radiometers can reach 0.041K while the integration time is 20ms.Based on the 3～22GHz detector,a bandstop filter is designed to realize the 2.75～20GHz radiometer,of which the temperature sensitivity can reach 0.066K@20ms.Secondly,a F-band low-noise amplifier is developed in this thesis.Its gain in98～138GHz is greater than 27d B,the noise figure in 98～110GHz is less than 6.6d B.The low-noise amplifier could work as a part of an F-band superheterodyne radiometer.Finally,this thesis uses the developed two sets of wide intermediate frequency radiometers and the existing 214GHz and 330GHz mixers in the laboratory to build and test the terahertz wide intermediate frequency superheterodyne radiometer.The2.75～20GHz radiometer is used as the intermediate frequency link of the 214GHz radiometer,and the temperature sensitivity of the terahertz radiometer is 0.52K when the integration time is 20ms;the 3～22GHz radiometer is used as the intermediate frequency link of the 330GHz radiometer,of which the temperature sensitivity can reach 0.37K when the integration time is 20ms.What’s more,with the designed 330GHz radiometer,a passive imaging system is built to complete the imaging experiment and realize hidden small metal targets detection.