Study On Thz Subharmonic Mixer Based On The Schottky Diode

The terahertz wave is located between the microwave and the infrared.Because of its special location,terahertz wave combines the characteristics of microwave millimeter wave and light wave.So the terahertz wave has broad application prospects in the fields of communication,imaging and exploration.In recent years,terahertz has attracted the attention of many scholars.Various research results have been published.As terahertz technologies matures,some of them have gradually translated into products that are changing people's life.In terahertz transmission and reception system,the mixer as a key device for frequency conversion has very important research value.In this thesis,two subharmonic mixers based on a Schottky diode have been introduced.In this thesis,we firstly introduced the research status of Schottky diode-based mixers at home and abroad.Then the working principle of Schottky diode mixer is analyzed.Based on this,we discuss the modeling of the Schottky diode in the terahertz band,mainly through developing the diode's local oscillator model and the linear model.The traditional design method is to divide the mixer circuit into several units.Then each unit will be designed separately.Finally we match each unit circuit to form the entire mixer circuit.In a comprehensive design method,the circuit is further broken down into transmission lines or waveguide units.Then we establish a complete mixer equivalent circuit model and complete the circuit matching and performance optimization in the overall model.The unit circuit in the traditional design method can be used in other circuit designs in the same frequency band.Compared with the traditional design method,the comprehensive design method has the advantages of shorter design cycle and higher flexibility.Finally,we designed two sub-harmonic mixers operating at 330 GHz and 220 GHz through these two methods.The final results are as follows,the frequency conversion loss of 330 GHz subharmonic mixer is better than 7.7dB,in the radio frequency range 298GHz-353 GHz.Through the down-conversion test,the single sideband conversion loss of 330 GHz subharmonic mixer is better than 13.4dB,the best conversion loss 7.7dB,in the RF 318GHz-352 GHz range.The simulation results of 220 GHz subharmonic mixer are as follows: in the local oscillator 100GHz-120 GHz range,the local oscillator echo is better than 7dB and the conversion loss is better than 8dB.The RF echo is less than 10 dB in the range of 200GHz-240 GHz.The test results of 220 GHz subharmonic mixer show that the frequency conversion loss is around 6-12 dB in the RF 198GHz-238 GHz range.