Terahertz Key Technology And Its Radiometer Application

Terahertz wave is an electromagnetic wave in the frequency range of 0.1 THz to 10 THz.Its frequency spectrum lies between microwave and light wave,and has the advantages of them both.It is the current technology frontier with significant scientific value and strategic demand recognized by the international academic community.A series of unique characteristics of terahertz wave make it have a great application prospect,can be widely used in atmospheric and environmental monitoring,high-speed wireless mobile communications,safety inspection,radio astronomy,etc.As one important application of terahertz technology,terahertz radiometer has the advantages of high resolution,security,and sensitivity,and can provide effective technical means for the detection of atmospheric components.It can be widely used in the research of atmospheric science,environmental monitoring,and disastrous weather forecast,and is a priority development technology in the “13th Five-Year Plan” of the National Natural Science Foundation of China.Based on the solid-state terahertz circuit technology,this dissertation focuses on the realization of the terahertz radiometer,starting with the modeling research of Schottky diode,and makes deep research on the integration of two key circuits(harmonic mixer and tripler)of the radiometer.Based on this,the experimental verification system of the terahertz radiometer is built,and the integration of the radiometer is preliminarily studied.The research content of this dissertation is embodied in the following three regards.(1)Terahertz harmonic mixers.The harmonic mixer is the frequency conversion module in the radiometer,plays the function of moving the radio frequency signal to low frequency.It is the key component to realize the system noise reception and plays a decisive role in improving the system performance.Especially in the terahertz band,due to the lack of solid-state amplifiers,the mixer directly determines the performance of the entire system.This dissertation analyzes the physical mechanism and non-linear characteristics of Schottky diodes and studies the main parasitic parameters of Schottky diodes in the terahertz frequency band.A three-dimensional accurate electromagnetic model of the diode is established,and its influence on the parasitic parameters is studied.Combined with the parasitic parameter analysis,the diode structure is optimized,and a diode structure of the small package,vertical deep channel and large width air bridge is proposed.A circuit optimization procedure based on the combination of “field” and “circuit” is proposed to improve the efficiency of circuit optimization.The core of the methodology is to split the whole circuit into sub-circuits according to its function and combine the linear electromagnetic characteristics of sub-circuits in the HFSS with the ideal nonlinear model of diodes in the ADS for circuit optimization.The GaAs monolithic integration and heterogeneous integration techniques are used in the THz harmonic mixing circuit,which improves integration of circuits.Based on the beam lead technology on GaAs substrate,the coplanar waveguide is applied to THz harmonic mixer,and a silver glue-free circuit package is realized by hot pressing grounded metal,which can improve the circuit consistency.The basic principle of the high-order harmonic mixer is studied,and the corresponding circuit is proposed for different harmonic times,realizing a breakthrough in the performance of the higher-band terahertz harmonic mixer.Finally,the experimental platforms are built to experimental research for various harmonic mixers.(2)Terahertz GaAs monolithic integrated frequency Tripler(×3 multiplier).Frequency multiplication based on the Schottky diode is an important technique to produce terahertz frequency source.In this part,a three-dimensional electromagnetic model of the varactor is established based on its working principles,and the effects of varactor main parasitic parameters on the Tripler performance are analytically investigated.Based on the analysis results,the structure size of the varactor pair for the 260GHz-300 GHz Tripler circuit is designed.A 260GHz-300 GHz Tripler frequency circuit structure based on a coplanar waveguide transmission line is proposed by using 12?m GaAs monolithic integrated technology,and a silver glue-free circuit package for the Tripler is realized by hot pressing metal bonding technology.The Tripler is machined,assembled and measured.The measurement results show that the Tripler has a peak efficiency of 8%,when the input power is 10 mW.When the input power is 120 mW,the Tripler has an output peak power of 4.9mW,and the frequency efficiency is 4.08%.The experimental results are in good agreement with the predictions,which demonstrates the effectiveness of the modeling of the varactor,the design of the Tripler circuit and the circuit optimization methodology as well.(3)Terahertz radiometer.On the basis of the terahertz key circuit realization,two radiometer experimental verification systems respectively working at 380 GHz and 582 GHz were successfully accomplished.And the experimental research was carried out using Y-factor measurements.In the 380 GHz radiometer,the equivalent noise temperature is 3024.6K,when the integration time is 20 ms and the before detection bandwidth is 120 MHz,the brightness temperature sensitivity is 3.89 K.In the 582 GHz radiometer,the equivalent noise temperature is 2756.4K,when the integration time is 20 ms and the before detection bandwidth is 120 MHz,the brightness temperature sensitivity is 3.22 K.