Research And Application On The Terahertz Source Based On Solid Circuit

As a research hot spot at present, Terahertz technology has been applied in different fields. Especially, terahertz source is one of the key technologies. Because domestic relevant research starts late and is limited by the semiconductor technology, many technological difficulties still exist. So far the terahertz systems on satellite are mainly imported from abroad. Based on the above background, this article makes a study of Local Oscillator, which is an important part of terahertz receiver front. Furthermore, research focuses on the design of terahertz frequency multiplier: it is a technical difficulty in the Local Oscillator. The main works in this article are as follows:1, Modeling and modificating of Schottky diode in terahertz band. The principle of frequency multiplier is use of the Schottky diode’s nonlinear, so the modeling of diode is extremely important in the design of multiplier block. Firstly, three dimensional geometrical modeling of planar Schottky diode is built in the article. Then corresponding circuit modeling is also built based on the operating principle. Actually, the parameters of diode used in the circuit modeling can be extracted through the measured I-V and C-V curves. Finally, the diode model is modificated in combination with the measured results.2, Research on the design method of terahertz multiplier. Due to increasing frequency, the parasitic caused by diode’s geometric package has a great impact on the performance of circuit. A method is adopted by combining field and circuit analysis. The field method based on vector finite element method make a full-wave analysis of 3D model to evaluate the affects of parasitics, while the circuit method based on harmonic balance method can make a nonlinear analysis and optimization of the whole circuit. To translate the field model to equivalent circuit model, that both of them are used in this method, it is necessary to analyse and extract the discontinuous structure. Finally, a terahertz tripler with anti-parallel has been developed to verify the above-mentioned method.3, Development of a teraherz source. The operating frequency of Local Oscillator are 225 GHz and 332 GHz. Actually, research focuses on the frequency multiplier at the last stage. In the 225 GHz Local Oscillator, the last stage is a tripler, while in the 332 GHz Local Oscillator, the last stage consists of two cascaded doubler. According to the level of domestic processing technology, the 225 GHz tripler based on discrete device uses the unbalanced structure because the diodes can be biased and thus the efficiency can be improved. The measured result shows that the output power more than 5mW in 215~228GHz. The maximal output power and highest efficiency are 17 mW and 7.1% respectively. For the last stage of 332 GHz Local Oscillator, the 166 GHz source is a four-way power combined doubler to realize high output power. The demands on the 332 GHz doubler is high efficiency. To the independent 166 GHz doubler: the measured maximum output power is 27.2mW and the highest efficiency is 19%. The measured maximum output power of 332 GHz doubler is 1.4mW and corresponding efficiency is 2.1%.4, Design of terahertz multiplier based on monolithic circuit. Because the multiplier with discrete device has many limits and is effected by assembly easily. This paper makes a study on monolithic circuit based on GaAs substrate. The parameters of Schottky diode are analysed and conformed at first. Then design a Schottky diode and its cut-off frequency is 1.5THz. Finally, design a 212 GHz doubler monolithic circuit based on the above mentioned diode, and the simulated highest efficiency is 37.6%.5, Designing and testing a terahertz band radiometer system. The 440 GHz real-aperture radiometer has been built and each part of system is developed by our research group, that the Local Oscillator is the 225 GHz source introduced before. This system can work steadily for a long time, and the measured system noise temperature is about 1800 K by using Y factor method. Furthermore, a 440 GHz synthetic aperture radiometer with two elements has been developed based on above mentioned radiometer unit. Later the phase accuracy measurement and single point source imaging experiment have been accomplished.