Research On Terahertz Up And Down Mixer

The terahertz wave with wavelength of 30um-3000 um is between visible light and microwave millimeter wave.It has many advantages and has a wide application prospect in environmental monitoring,radio astronomy,broadband communication,precision guidance,satellite communication and so on.In terahertz communication technology,terahertz mixer is used to achieve the frequency shift between baseband signal and THz band RF signal.The terahertz mixer realized by harmonic mixing can make the frequency of the local oscillator signal only 1/n of the radio frequency signal,which solves the problem that the local oscillator signal source in the terahertz band is difficult to obtain.In this paper,we study a terahertz mixer which can output the 375 GHz radio frequency signal by mixing the Ka band intermediate frequency(IF)signal with the W band local oscillator signal and can output the Ka band IF signal by mixing the received 375 GHz radio frequency signal with W band local oscillator signal.The wavelength of the electromagnetic wave in the terahertz band can be compared with the size of the Schottky diode package.It will produce parasitic effect.It is difficult to extract accurate parasitic parameters to ensure the design accuracy.Therefore,this paper uses a threedimensional electromagnetic model of diode core package to simulate the parasitism of the Schottky diode.We employ the method by combining the three-dimensional electromagnetic model established in HFSS with the diode SPICE parameter model in ADS to simulate characteristics of the diode.In the design process,considering the fabrication difficulty and cost performance,the mixer is fabricated on two substrates.The circuit of the radio frequency part and the local oscillator part is realized on a quartz substrate with a thickness of 50 um.The circuit of the IF part with low frequency(LF)band which allows a large tolerance range is realized on the duroid 5880 substrate with a thickness of 0.127 mm.The interface of the mixer circuit adopts waveguide interface,where the RF port uses WR2.2 waveguide,the local oscillator port uses WR10 waveguide,and the intermediate frequency port uses WR28 waveguide.The simulation result shows that the up-conversion mixer can achieve the 14 dB conversion loss in the frequency band of 370-380 GHz,and the down-conversion mixer can achieve the frequency conversion loss of 14 d B.The circuit size of the terahertz mixer is very small.In the process of fabrication,it is necessary to consider the problems such as the assembly mode of quartz substrate and reducing the effect of machining error on the circuit performance.Mixer is an important part of the communication system,so the 375 GHz terahertz mixer researched in this paper has a significant impact on promoting the development of terahertz technology in the communication field.