| As a hot field of current academic research, terahertz (THz) technology can beused in the areas close related to national economic and social development, such asobject imaging, environmental monitoring, medical diagnostics, radio astronomy,security check, counter-terrorism detection, satellite communications and radardetection.Nowadays, applications of THz technology in China are still at their initial stagesand breakthroughs in many key techniques have not been made yet. With keytechniques such as theories of THz semiconductor devices, circuit modeling methods,simulation techniques and their means of implementation as the jumping-off points, thedissertation aims to develop the core circuits in the applications of THz systems andmake breakthroughs in key techniques of such applications, and the study in thisdissertation will lay a theoretical and technical foundation for the development of THzkey circuits and promote the researches and applications of THz systems.THz frequency doublers and mixers are crucial front-end circuits of THz systems,and their functions determine the performances of THz transceiver systems. So, thedissertation carries out studies on low loss sub-harmonic mixers and high-performancefrequency doublers working in THz frequency band. The study has madebreakthroughs in several core technologies, such as the analyzing technology of theparasitic parameter of the diode packages and the construction technology ofthree-dimensional electromagnetic model of the diode packages. Moreover, ahigh-performance THz sub-harmonic mixer and a solid state THz frequency doublerare developed, which lays a theoretical and technological foundation for theapplication the THz system. Meanwhile, the dissertation also studies the application ofspace mapping algorithm in the fast design of THz filters and develops relevant circuits,which lays a technical foundation for space mapping algorithm to be applied in thedesign of THz passive circuits.This dissertation mainly engages in the following tasks and the results of theresearch are mainly reflected in: 1. In the research of terahertz sub-harmonic mixer, a fast and accurate analysismethod for parasitic parameters of diode package has been put forward and a relativelyaccurate model of Schottky diode circuit has also been built. In THz frequency band,accurate modeling of Schottky diode is essential to the development ofhigh-performance mixer. Since the influence of the Schottky diode package parasiticparameters on the performance of the mixer has become very obvious, in order to takethe influence of parasitic parameters into account and achieve accurate design for themixer, a rapid and accurate way to analyze parasitic parameters of the diode is putforward. Next, a Schottky barrier reverse parallel diode pair in W-band provided byVDI company is adopted, and an analysis of its related parameters is made, then arelatively accurate circuit model according with such diode is established. Finally, aW-band second sub-harmonic mixer is developed based on the circuit model. Throughthe experimental study of the mixer, the diode model established in accordance withthe method of parameters analysis is proved to be accurate and reasonable, providingan efficient theoretical method for producing THz sub-harmonic mixers.2. In the research of terahertz frequency doubler, a three-dimensionalelectromagnetic model based on packaging of diode physical structure has beenconstructed and a relatively accurate varactor nonlinear model has been established aswell. The development of high-performance THz doublers lies crucially in accuratemodeling of frequency doubling tube and reasonable circuit structures. The circuitstructure built by feeding the input electromagnetic signal energy at the input end ofthe frequency doubler into the frequency doubling tube through space coupling willenable the frequency doubler to achieve high performance, and the circuit structure issimple and easy to process. Meanwhile, the realization of such circuit structure needsto be based on accurate three-dimensional electromagnetic modeling of varactor arraypackages. Therefore, this dissertation firstly focuses on the extraction method ofstructural and material parameters of the semiconductor structure in the diode as wellas the modeling method of nonlinear model of Schottky varactors. Then, technicalschemes of frequency doublers for the frequency at170GHz,190GHz and220GHzrespectively were put forward, based on the liner and nonlinear models of Schottkyvaractor, and precise optimizations of the circuit of the frequency doubler at the threefrequencies are done by simulations. Finally, two frequency doublers for the frequencies at190GHz and220GHz are built, and the220GHz frequency doubler isexperimentally researched, showing that the doubler has a maximum output power of3.2mW. The experiment results prove the correctness of the three-dimensionalelectromagnetic model of the THz varactor package and the reasonableness of thefrequency doubler circuit, and build the technical basis of the studies of frequencydoublers at THz frequency band.3. The Scale Model Theory was used to apply the space mapping algorithm tocircuit design for high-performance filter in millimeter wave/THz frequency band. Thegeometric proportion scale model is adopted to amplify the millimeter wave/THzfrequency band circuit up to microwave frequency band with equal proportion, and thelibrary in ADS platform is used to build up the circuit model of millimeter wave/THzfrequency band filters, then the rapid and accurate design of millimeter-wave/THzfrequency band filters is realized through building optimization and parameterextraction circuits in ADS. Based on this method, an example of the developingprocesses of an improved hammerhead filter and a CMRC filter are given, to elaboratethe applicational ideas of space mapping algorithm. Through the comparison betweenthe results from space-mapping optimizations and the ones obtained directly from theelectromagnetic simulation software, the dissertation proves that space mappingalgorithm can remarkably improve the design efficiency on the premise of ensuring theprecision. Meanwhile, it also proves that the space mapping method can be applied indeveloping millimeter-wave/THz passive circuits for higher frequencies. |
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