| Terahertz wave has many excellent properties and great application potentials.The primary problem in terahertz technology research is how to obtain terahertz sources.Frequency multiplying of microwave and millimeter-wave signal to higher frequencies based on nonlinear effects of solid-state devices is one of the main technical approaches to obtain terahertz signal.Planar Schottky diodes continue to be the mainstream devices in terahertz solid-state frequency conversion(frequency multipliers,frequency mixers and detectors)technology due to their low parasitic parameters,high cut-off frequency and ability to operate at room temperature.Terahertz Schottky diodes for frequency multipliers often work in high frequency,high power,nonlinear and multi-harmonic states.At the same time,along with complex working conditions,some special physical effects will appear inside the diodes,including self-heating effect,speed saturation effect,etc.Therefore,one of the main challenges in terahertz frequency multiplication technology is how to accurately model diodes.Traditional diode SPICE model does not consider these special physical effects,resulting in poor model accuracy.As the frequency increases,how to optimize the diode design according to operating frequency is also a key issue.At the circuit design level,a large number of mode conversion and filtering structures are required in terahertz frequency multiplication circuits.These passive circuits also have an important impact on the performance of frequency multipliers.On the other hand,in the terahertz band,broadband design of frequency multipliers is also a recognized technical difficulty.Focusing on the above key problems,this dissertation has made an in-depth sduty on the aspects such as self-heating effect,velocity saturation effect,parasitic parameters extraction,diode frequency adaptability,broadband matching method,novel waveguidemicrostrip mode conversion,harmonic control matching technology,and terahertz monolithic integration technology.The main research contents include:(1)Research on intrinsic model of terahertz Schottky barrier diodes.Aiming at the low accuracy of the traditional diode SPICE model,this dissertation characterizes the self-heating effect and velocity saturation effect of the diodes at high frequency and high power based on electro-thermal simulation and fitting function,and proposes a diode physics-based model.In addition,the model also corrects the forward C-V characteristics of the diodes based on physics-based simulations.The frequency multipliers designed with the diode physical-based model proposed in this dissertation has a better agreement between the measured results and the simulated ones.Besides,the modeling method also has a good generality.(2)Research on parasitic model of terahertz Schottky barrier diodes.Aiming at the diode structure optimization problem,a method for extracting parasitic parameters using four structures based on odd-even mode theory is proposed.Combined with matrix operations,the method can quickly and accurately extract the equivalent parasitic parameters of the diode,which helps to guide the structure optimization and design of the diodes.In terms of 3D electromagnetic modeling,in view of the inconsistent issue of the number of ports in traditional coaxial-like internal port technique,this dissertation proposes a dual lumped port technique with a clear physical meaning,which can be used to replace the classic coaxial-like port technique with a higher accuracy.(3)Research on diode frequency adaptability and broadband matching method.In this dissertation,the frequency adaptability of the diode is studied based on statistical methods,and the corresponding statistical equations are obtained.Starting from the basic principle of circuit matching,this dissertation studies the limiting factors of diode broadband matching and proposes an impedance compression matching technique(ICMT)to expand the operating bandwidth of frequency multipliers.Based on the proposed statistical law and broadband matching method,two frequency doublers with full waveguide bandwidth are developed,covering the 140-220 GHz and 170-260 GHz bands,respectively.The former possesses average output power of 1.5 m W and the latter delivers an average output power of 5-7 m W.(4)Research on terahertz novel waveguide-microstrip mode transitions.The design of terahertz frequency multipliers requires a large number of waveguide-to-microstrip(WG-to-MS)transitions.In addition,in some special occasions,a dirct current/intermediate frequency(DC/IF)return path is also necessary.In order to make the terahertz frequency multipliers possess a more compact structure,three novel WG-to-MS transitions are proposed and verified,including WG-to-MS with a built-in DC/IF return path,WG-to-MS inline transition using a wedge-waveguide iris and WG-to-MS inline transition with a loop grounding resonator.Using the above novel transition structures,three compact terahertz frequency multipliers are developed,including a 110 GHz frequency tripler,a 140 GHz frequency doubler,and a 220 GHz frequency tripler.Based on the above frequency multipliers,a 220 GHz security inspection imaging front-end was built,and good imaging results were obtained.(5)Research on probe-based multi-harmonic matching technology.The matching of frequency multipliers in the terahertz band is mostly based on high-loss microstrip circuits.At the same time,the impedance states of idle harmonics are often ignored in traditional design methods.In order to reduce the matching loss and improve the frequency conversion efficiency,a probe-based multi-harmonic matching technology is proposed.By optimizing the structural parameters of the transitions,the probe can realize the matching of the diode and the controlling of the idle harmonics while completing mode conversion.Using the proposed matching method,three terahertz frequency multipliers are developed,including a 170 GHz doubler,a 250 GHz tripler,and a 500 GHz tripler.The three frequency multipliers achieved a peak output power of 13.22 m W,6.3 m W,and460 ?W,respectively.Furthermore,based on the above frequency multipliers and an existing 500 GHz subharmonic mixer,a 500 GHz terahertz frequency conversion frontend was built to realize the up and down conversion of the spectrum.(6)Research on terahertz monolithic integrated frequency-multiplication technology.Aiming at the difficulties of large assembly errors and poor consistency in the traditional hybrid integrated frequency-multiplication technology due to manual assembly.This dissertation continues to carry out the research on the terahertz monolithic integrated frequency-multiplication technology.Monolithic integration avoids manual assembly errors by integrating diode devices and passive circuits on a single substrate.Using domestic monolithic process,a 500 GHz frequency tripler was developed.The 500 GHz frequency tripler operated in the 460-540 GHz frequency band with an average output power of 250 ?W. |
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