| Terahertz(THz)communication technology,as the key to unlocking the future 6G(the sixth generation mobile communication technology)high-speed communication,has become one of the major scientific research directions in the field of communication and information science.The terahertz direct modulation technology is expected to realize high-speed and large-capacity data transmission and fast beam scanning,which plays an important role in promoting the application of terahertz communication and imaging systems.Many core devices such as terahertz sources with high power capacity and highspeed modulation of terahertz waves have become the core and urgent key technologies in the field of terahertz application.In addition,the terahertz system has put forward new requirements for the integrated miniaturization of modules for practical applications.This dissertation mainly focuses on the key devices of terahertz communication based on direct modulation.The related research in this dissertation aims to promote the development of domestic terahertz high-speed communication and provide good technical support for the integration and miniaturization of key terahertz devices.The main work and innovations of this dissertation are shown as follows:(1)Aiming at the problem that the model is not accurate due to the temperature rise of diode junction in the terahertz source with high power capacity,in this dissertation,the temperature factor is introduced on the basis of the traditional Spice model and equations of nonlinear junction parameter are modified.Thus,a SDD(Symbolically Defined Devices)nonlinear model of Schottky diode based on thermal effect is established in the terahertz frequency band.Based on this model,the terahertz monolithic integrated frequency doublers with even-pair of cascaded multi-die are studied.By studying the relationship between the physical structure of the monolithic diode and the parasitic parameters,physical models of the monolithic diode with even-pair of cascaded multidie and corresponding peripheral matching circuits adapted to 0.17 THz and 0.34 THz for the integration are independently designed respectively.And the terahertz monolithic integrated frequency doublers of 0.17 THz and 0.34 THz with even-pair of cascaded multi-die are successfully developed.The experimental results show that the input power of the 0.17 THz frequency doubler can withstand 300 m W with an 8-die monolithic diode,achieving the highest power output of 82 m W;the 0.34 THz frequency doubler with a 6-die monolithic diode has an output peak power of 20 m W at an input power of about 120 m W,and the peak efficiency is 17.4%.Compared with the traditional Spice simulation model,the overall average consistency of the SDD model is improved by 61% and 50%respectively,which verifies the reliability of the SDD nonlinear model.This achievement effectively promotes the development of the technology of domestic high-power terahertz monolithic integrated frequency multiplier.(2)Based on the nonlinear model of terahertz Schottky diodes,under the existing domestic terahertz monolithic integration process,two-stage frequency multipliers with cavity integration and on-chip integration are studied,and a 0.34 THz small cavityintegrated 2×2 frequency multiplier is developed,realizing the miniaturization of the domestic terahertz front-end frequency doubling source.In order to compactly integrate the two-stage frequency doubling chip into the cavity and realize inter-stage impedance matching,a method using distributed equivalent circuit is proposed,and the whole frequency doubling circuit is decomposed into several sub-unit circuit models.The interstage matching waveguide is optimized through full-power active simulation.The experimental results show that when the input power is about 300 m W,the overall output power is above 8 m W in 0.334 THz～0.343 THz band;the maximum output power is 14.1m W at the 0.32 THz,and the frequency doubling efficiency reaches 5%,which is basically consistent with the simulation results.The 0.34 THz two-stage on-chip monolithic integrated frequency multiplier is studied,and the two-stage chip can be fed at the same time by rationally designing the number of two-stage dies of diodes.The interstage harmonic isolation is realized by using the wide microstrip branch structure for the second-stage doubler.The simulation results verify the feasibility of the on-chip integrated 2×2 frequency multiplier.(3)The terahertz phase reconfigurable planar lens with tunable terahertz focal lengths is verified through simulation research and experimental tests based on the manipulation of the amplitude or phase of terahertz waves by spatial array artificial microstructures.On this basis,the electronic transport of the Schottky diode,the electromagnetic resonance characteristics of the artificial microstructure and the THz wave transmission mode on the chip are innovatively combined,the terahertz high-speed modulation meta-chip for on-chip transmission is proposed that combines fin lines with microstructural units of nested Schottky diodes.The modulation mechanism of the terahertz wave amplitude based on the 0.34 THz on-chip resonant microstructure unit composite Schottky diodes is studied.The design idea of physical field resonance mode combined with circuit matching is proposed,and a high-speed terahertz amplitude modulation chip is developed.Under the dynamic test,the overall flatness of the modulation rate is relatively good within 27 GHz,and the maximum data transmission rate can reach 25 Gbps.The terahertz direct modulation communication system based on this modulation meta-chip realizes 4K video transmission,which verifies that the developed meta-chip has good performance.(4)On the basis of the breakthrough of key circuits of terahertz direct modulation,a scheme of solid state integrated circuit of terahertz(2×2)two-stage frequency doubling combined with modulation based on Schottky diode is proposed.And a small integrated module based on 0.34 THz frequency doubling-modulation is further developed.The doublers and modulation chips are compactly integrated into the cavity.Through simulation research,the overall structure is optimized,and the problem of inter-stage chip impedance matching is solved.The experimental tests prove that the module of 0.34 THz frequency doubling-modulation realizes the dynamic control of output power in0.330～0.343 THz band,and the switching ratio reaches 20 d B,which is basically consistent with the simulation results.For the single-tone sine wave signal,the modulation rate is 25 GHz;when the digital baseband signal is loaded,20 Gbps highspeed data transmission is realized at the 0.34 THz carrier frequency.Experiments show that the module has the ability of adjustable output power and high speed data transmission. |
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