Research On Millimeter-wave And Terahertz Mixing Technology

Compared with microwave, millimeter-wave possesses the characteristics of short wavelength, wide band, large information capacity and other advantages. Nowadays, as the microwave spectrum is becoming more and more crowded, the working frequency of various electronic systems has been gradually extended to the millimeter-wave band. It is important to research the precise design methods of millimeter-wave devices due to their practical applications. Terahertz wave is the only electromagnetic spectrum which has not been fully exploited. Its long wave band coincides with the microwave and millimeter-wave, and its short wave band coincides with the infrared wave, so the terahertz wave has the advantages of both millimeter-wave and infrared wave. Terahertz wave has broad application prospects in many fields, such as broadband communication, precision guidance, object imaging, environmental monitoring, medical diagnosis, etc. Consequently, it is significant to master the terahertz cutting-edge technology for national defense and civil projects. As the core device of receiver and transmitter front-ends, mixers are widely used in communication, radar and other millimeter-wave and terahertz systems. Mixing technology is a key research direction of millimeter-wave and terahertz technology.In this dissertation, based on the millimeter-wave and terahertz precise modeling of the planer Schottky barrier diode(SBD) and the circuit design method which combines linear and nonlinear simulation, several millimeter-wave fundamental mixers, two 220 GHz sub-harmonic mixers, two 330 GHz fourth harmonic mixers and a terahertz front-end using 220 GHz sub-harmonic mixer are proposed. The main research contents are as follows:(1) Study on modeling technology of the millimeter-wave and terahertz planar SBD. Based on the physical mechanism, structural characteristics and production process of the planar SBD, a SBD millimeter-wave equivalent circuit model including the diode’s parasitic effects is proposed by expanding the SBD intrinsic SPICE model in order to solve the problem of the inaccurate intrinsic SPICE model because of the inability of model the parasitic phenomena of the SBD structure and package in the millimeter-wave and terahertz bands when frequency increasing. The finline mixer cannot be easily simulated by using the SBD equivalent circuit model and CAD software, so a substitution model based on the SBD impedance is proposed and the simulation method of designing finline mixers using the proposed substitution model is studied. The more accurate three dimensional electromagnetic model of the SBD is further suggested. Three ways to build the 3D electromagnetic model are proposed,which have achieved the accurate modeling of millimeter-wave and terahertz modeling technology of the planar SBD.(2) Study on the design method of mixer. The field-circuit co-simulation method which combines linear and nonlinear simulation is explored. The mixers in this dissertation were precisely designed according to the systematic design method of the mixer based on the subsection design method and the synthesis design method.(3) Study on millimeter-wave fundamental mixers. In the design of 60 GHz finline mixers, the SBD substitution model is used and the groove matching circuits are proposed, which have solved the problem that finline mixers cannot be easily simulated by CAD software. Additionally, in the design of 94 GHz mixers, one finline mixer with double coupling bandpass filter, one with three parallel lines bandpass filter and one without bandpass filter are proposed through the establishment of SBD 3D electromagnetic model. Compared with the substitution model, more accurate simulation results of finline mixers are obtained. An improved crossbar bridge is proposed and used in the 94 GHz crossbar mixer, which has the advantages that the improved crossbar structure can be used as a unit circuit, the position of SBD is controllable and the loss is smaller compared with the conventional crossbar bridge. A 94 GHz ring mixer based on five-port microstrip ring bridge structure is proposed to avoid the jumper structure of the traditional four-port ring mixer. The measured results of the millimeter-wave fundamental mixers are in good agreement with the simulated results and the excellent performances are obtained, which have verified the feasibility and accuracy of SBD modeling technology, and laid a solid foundation for the design of mixers at higher terahertz frequency.(4) Study on terahertz sub-harmonic and forth harmonic mixers. Due to the characteristics of extremely short working wavelength and ultra-small circuit size of terahertz mixer, it will generate complicated parasitic effect and lead a limited optimizing space for circuit matching in the terahertz design. Dealing with these problems, the precise 3D EM planar SBD model is established and the synthesis design method for terahertz mixer design is adopted. The research of 220 GHz subharmonic mixer is carried on exploiting the method and model mentioned above. The measured results show that the conversion losses of the mixer based on the synthesis design method are less than 9dB from 212 GHz to 226 GHz and the minimum value is 6.9dB. The proposed mixer has reached the same level of similar products in the world. A narrow band and a wide band 330 GHz forth harmonic mixer using the synthesis design method are proposed. The measured results show that both mixers have good performances. Besides, a terahertz up and down conversion system using 220 GHz sub-harmonic mixers is introduced, and the experiment of terahertz signal propagation using the terahertz system is performed.