Research On The Key Terahertz Passive Components

Terahertz(THz)wave,which is between microwaves and infrared light waves,is the only electromagnetic spectrum which has not been fully exploited,and becomes a frontier and hot issue in the academic research.As the essentials of the THz system,terahertz key passive components,such as THz filters and couplers,are the fundamentals of development and application of THz waves,which have become the Terahertz technology research hotspot in recent years.Achieving the Terahertz filters and couplers with high performance is of great significance in the development of Terahertz systems.The essential features of conductors,the terahertz waveguide filters and couplers based on the MEMS,the low loss suspended dielectric waveguide and the terahertz waveguide switch based on the thermal actuators are intensively researched in this dissertation.The main research contents are as follows:(1)Researches on surface conductivity and impedance of THz conductors.Compared to the microwave band and millimeter-wave band,the skin depth of THz conductors reduces as the frequency increases.Furthermore,surface characteristics of conductor are affected more significantly by frequency,and are more sensitive to the surface roughness.Hence,the metal surface model of microwave and millimeter-wave band cannot accurately characterize the surface characteristics in the terahertz band.To deal with the problem,an improved Huray model is proposed.The terahertz metal surface characteristics are analyzed while considering the frequency and the surface roughness.And the scattering power is included in the computation of the metal surface of the total dissipation power.The improved Huray model makes up for a lack of accuracy of the traditional Huray model while predicting the rough conducting surface features in the THz or even higher frequency band.The Mie scattering model,HB model and Huray model of metal surface roughness model are studied,and the effective conductivity and surface resistance with frequency and surface roughness variation degree are further investigated.And then approaches of analyzing the rough metal surface conductivity and effective surface resistance are developed in the terahertz Band.Based on the studies above,the metal waveguide filters and couplers are realized,improving the designing accuracy.(2)Study of Terahertz waveguide filters based on MEMS technique.The quality factor of waveguide resonators is generally small due to the effect of the metallic surface roughness.Besides,the sensitivity of frequency response to the small size of filter structures is significant,leading to a low error tolerance and a high dependency to the machining process of the components.According to the study of the field distribution of resonate modes and the quality factor of resonator,as well as the relationship between the surface roughness and the power loss,the approach for realizing the high quality factor with low loss of THz metallic waveguide is proposed.Moreover,the CT cross-coupling structure is adopted to improve the error tolerance of the filters.By introducing the transmission poles,both of the insertion loss within pass-band and the rejection outside the pass-band are improved without increasing the number of resonators.The TE301/TE102 dual mode inductive coupling filter is also employed to improve the rejection outside the pass-band.The effect of MEMS process brought to the performance of filters is analyzed as well,which optimizes the design of filters.Based on the studies above,a silicon MEMS waveguide filter is developed.The measured insertion loss is less than 2dB and the rejection outside the pass-band is better than 30 dB 1.67% away from the center frequency.(3)Study of Terahertz waveguide couplers based on the MEMS technique.The Terahertz waveguide couplers generally have the small size,which is 4~5 times less than the size of measuring waveguides interface.Four input/output waveguides should be extended to an enough length while utilizing the traditional measuring method.Because the waveguide loss cannot be ignored in the terahertz frequency band,traditional measuring method is not accurate.Dealing with this problem,a low loss measurement method for terahertz 4-ports coupler is proposed.Three measuring structures are designed for measuring the through,coupling and isolation where the input and output waveguides are kept in a relatively short length compared with traditional measuring structures.Based on the silicon MEMS technology,an E-plane Quadrature-Hybrid coupler with coupling of 3d B and a H-plane short-slot Riblet-type coupler with coupling of 3dB are fabricated and measured.The measured average insertion losses of two couplers are better than 1dB,which verify the accuracy of the proposed measuring method.(4)Research on low loss THz dielectric waveguide.In most cases,the metal waveguide loss cannot be ignored in terahertz band.By investigating the propagation modes and the loss of dielectric waveguide,a suspended silicon rectangular waveguide of low loss is proposed at the 590GHz~655GHz frequency band.A piecewise-tapered transition structure is proposed as the transition between silicon waveguide and metallic waveguide.The periodic gratings are utilized to sustain the silicon waveguide.By utilizing the mentioned configuration,the electromagnetic fields could be bounded in the silicon waveguide.The measured average insertion loss is better than 0.1dB/mm,which is less than the loss of metallic rectangular waveguide.(5)Study of Terahertz waveguide switch based on the MEMS thermal micro-actuators.Switch is the important component in the terahertz waveguide system.The terahertz switches are usually based on the photonic crystal,frequency selective surface structures,which are not convenient to connect to the waveguide system.In this dissertation,a terahertz waveguide switch based on the thermal micro-actuator is proposed.The MEMS thermal micro-actuators are directly integrated in the terahertz metal waveguide.Based on the approach of analyzing the electromagnetic fields in the waveguide,the key parameters of thermal micro-actuator affecting the electromagnetic fields propagation such as the physical structure and rotation angle are investigated.Furthermore,horizontal and vertical postures of the thermal micro-actuator could be achieved by varying the temperature,resulting in the passing and blocking of the fields in the waveguide,which resolves the problem of integrating of the terahertz switch and waveguide system.At the 220~330GHz frequency band,the simulated insertion loss is better than 1.5dB while the thermal micro-actuators are flatting on the bottom of the waveguide,and the simulated insertion loss is about 90 dB while the micro-actuators are perpendicular to the bottom surface.