Research On Key Techniques Of 220GHz Radiometer Front End

With the development of terahertz technology,terahertz radiometer has been widely applied in the area of planetary atmospheric,anti-terrorism security,medical imaging and so on.The research on key techniques of the terahertz radiometer plays a great role in the applications of academic and engineering.In this thesis,the principle of radiometer and the key techniques of radiometer front end are introduced in detail,including blackbody radiation,radiometer characteristics,mixer,multiplier,planar Schottky diode and so on.The 220 GHz radiometer adopted the super-heterodyne full power type.Terahertz mixers are often used as the first-stage devices in super-heterodyne radiometer systems when lacking of terahertz low-noise amplifiers,of which the performance will directly affect the temperature sensitivity and stability of the radiometer.The study of high performance terahertz mixer and the frequency multiplier which provides LO for mixer is the key part in the design of terahertz radiometer.Based on the 3D electromagnetic model of GaAs Planar Schottky Diode,combing the two methods of “field” and “circuit”,a 220 GHz subharmonic mixer and a 110 GHz tripler have been designed.The reverse parallel diode pair structure is used in the design of the mixer to realize subharmonic mixing;and codirectional parallel diode pair structure is used in the design of 110 GHz tripler to achieve the purpose.When the driving power of the 110 GHz tripler is about 100 mW,the output power can attain above 5.5mW in the range of 104~111.5GHz by adjusting the bias voltage;and when the power of LO is about 5.5mW@110GHz,the frequency conversion loss of the 220 GHz subharmonic mixer is less than 12.2 dB in the RF frequency range of 215~225GHz and the best conversion loss is 9dB.When the pre-detection bandwidth is 5GHz and the integral time is 20 ms,the sensitivity of the 220 GHz terahertz radiometer is 1.08 K.The 220 GHz terahertz radiometer developed in this thesis can provide reference and experience for the future development of terahertz radiometer imaging system.