Research On Key Technology Of Terahertz Frequency Measurement Based On Harmonic Mixing

Terahertz signal has the characteristics of high frequency,wide bandwidth,narrow pulse,large energy attenuation in space,and low quantum energy.It can be applied to broadband communications,high-resolution terahertz radar,close-range military communications,indoor high-speed communications,and celestial bodies.Observation and weather monitoring,etc.Numerous application scenarios make terahertz technology a research hotspot in the field of science and technology today.Common devices that generate terahertz signal sources include optical quantum devices,semiconductor solid-state electronic devices,vacuum electronic devices,etc.The vacuum electronic devices represented by the gyrotron can generate highpower terahertz signals.How to accurately measure the frequency of the 1THz signal generated by the gyrotron in the subject is related to this article.According to the characteristics of the signal source under test,this paper designs a terahertz frequency measurement system based on harmonic mixing.The key technologies in the terahertz frequency measurement system are E-plane horn antenna and terahertz harmonic mixer..The E-plane horn antenna designed in this paper is integrated with the terahertz mixer cavity,which can reduce the processing cost.The antenna waveguide port is connected with the mixer's waveguide suspension microstrip line transition structure,which can efficiently integrate the space in the space.The terahertz signal is coupled to the planar transmission line circuit,in which the gain of the E-plane horn antenna is 14 d B.According to the terahertz frequency measurement system index,combined with the existing experimental conditions,a 6th harmonic mixer is designed,in which the Schottky diode pair is installed in the mixer circuit in a hybrid and integrated manner.Before designing the mixer circuit,the principle of harmonic mixing is deduced,and the design index of the frequency selective circuit in the mixer circuit is analyzed.In the HFSS software,the radio frequency module and the duplexer in the terahertz mixer circuit are designed in turn,the threedimensional model of the Schottky diode installed in the transmission line is established,and the S parameters are analyzed.Combined with the ADS simulation software,the circuit modules are jointly simulated and optimized,and finally the 6th harmonic mixer works stably in the frequency range of 922GHz?1300GHz.The conversion loss of the mixer is less than57 d B.When the terahertz signal frequency is 1THz,the local oscillator power When it is13 d Bm,the conversion loss of the mixer is 43 d B.Combining the design of the E-plane horn antenna and the 6th harmonic mixer model,the theoretical analysis of the entire frequency measurement system shows that the working performance of the terahertz frequency measurement system based on harmonic mixing is: the terahertz gyrotron signal frequency is 1THz,and the bandwidth is 200 GHz,power 0?100W,when the distance between the gyrotron and the antenna is 2m?5m,the system frequency measurement range is 922GHz?1300GHz,the bandwidth is 378 GHz,and the minimum frequency measurement error is ±0.026 GHz.The linear dynamic range of the frequency converter is-93 d Bm?10d Bm,and the input power range of the local oscillator signal is6.5d Bm?13d Bm.