Research On Above 500 GHz Sub-harmonic Mixer

As one of top important technologies that will change the future,terahertz technology has been becoming a hot research frontier in recent years.Terahertz superheterodyne receiver systems have broad application potential in communications,radar,material science,security applications,biomedicine,earth science,and astronomical detection.Terahertz mixer,as the core device of the terahertz transceiver system,is one of the most important components in the research of terahertz technology.This thesis studies mixers operating about 500 GHz based on planar Schottky barrier diodes.The main research contents are as follows:（1）Research on the Schottky diode model.The Schottky diode is introduced from the aspects of physical structure,working mechanism,and equivalent circuit model.Aiming at the problem that SPICE parameter model cannot describe the linear parasitic parameters of the diode,a three-dimensional electromagnetic model of the diode is added.And the three-dimensional electromagnetic simulation model is combined with the SPICE model to accurately represent characteristics of diodes in the terahertz frequency range.Finally,two mixers are designed and measured to verify the accuracy of the model.（2）Research on the design method of terahertz mixer.From the aspects of design principles,design ideas,advantages and disadvantages,three design methods for the terahertz mixer,including subdivision design method,global design method,and half-subdivision and half-global design method,are analyzed in detail.In order to solve the resonance phenomenon that is easy to occur in the design process of the global and half-subdivision and half-global design methods,this thesis proposes an improved half-subdivision and half-global design method for the design of a wideband frequency mixer.First,the unit circuit simulation is carried out according to subdivision design method.And then some unit circuits are divided into basic transmission line units according to the design requirements.Finally the overall circuit simulation is carried out.（3）The interconnection between the mixer and other devices.When most terahertz mixers are connected with other devices,offsets and gaps are prone to occur at the waveguide connection,which will increase the transmission loss between the devices.In this thesis,the low-loss connection between the mixer and other devices is realized by adding a choke flange at the waveguide input of the mixer.（4）The design,processing and testing of the mixer.A 530-590 GHz sub-harmonic mixer is designed by half-subdivision and half-global design method.The up-conversion test results show that: When local oscillator（LO）frequency is fixed at274 GHz,the double-sideband（DSB）conversion loss is about 8 d B in the intermediate frequency（IF）range of 0.5-30 GHz.In addition,a 460-540 GHz sub-harmonic mixer is designed by improved half-subdivision and half-global design method.In the radio frequency（RF）range of 460-540 GHz,the single-sideband（SSB）conversion loss is better than 8 d B,and the return loss is better than 10 d B.The down-conversion test results show that: in the RF range of 480-510 GHz,the SSB conversion loss is better than 15 d B,and the optimal conversion loss is 9.2 d B.The up-conversion test results show that: in the IF range of 1-40 GHz,the DSB conversion loss is better than 9 d B.