Research On Key Technologies Of 330GHz Passive Imaging System Front End

Terahertz wave is an electromagnetic wave in a frequency of 100GHz-10 THz.Its electromagnetic spectrum is between microwave and light wave.Therefore,it has the advantages of them both: wide bandwidth,high penetration,low quantum energy,etc.It has significant scientific value and strategic demand.Terahertz waves have broad application prospects in the fields of biomedicine,atmospheric environment detection,high-speed wireless communication,and security detection.In these applications,imaging technology has always been one of the research hotspots.The terahertz imaging system has the advantages of high carrier frequency,easy realization of wide bandwidth,high security,and high penetration of non-polar materials,which can be widely used in airport and subway security inspection,medical target detection and other fields.This article mainly studies the terahertz passive imaging system and gives more detailed introductions to the principle,system composition,and key technologies of the terahertz passive imaging system front end.In the absence of a good-performance terahertz low-noise amplifier,the terahertz mixer is the first-level device,which performance will directly affect the performance and stability of the imaging system.Therefore,the development of a high-performance terahertz mixer is the core link in the design of a terahertz passive imaging system front end.At the same time,adding a narrow-band filter between the local oscillator source and the mixer can reduce the noise introduced into the system by the local oscillator source,which has a certain optimization effect on the imaging system.In this paper,a 330 GHz sub-harmonic mixer is proposed by using the three-dimensional accurate electromagnetic model of the diode and the combined simulation method of "field" and "path".At the same time,after comparing the different structures,a 82.5GHz narrow-band E-face diaphragm waveguide filter is proposed.After experimental testing,when the RF frequency is in the range of 310-350 GHz,the conversion loss of the proposed 330 GHz sub-harmonic mixer is less than 12 d B,and the noise is less than 1800 K.The passband range of the proposed narrow-band E-face diaphragm waveguide filter is between 82 and 83 GHz,the suppression at 81 GHz and84GHz is greater than 15 d B,which meets the system requirements.Then the mixer and the first-stage low-noise amplifier are integrated to build a 330 GHz superheterodyne radiometer system.After experimental testing,the radiometer's brightness temperature sensitivity is 0.3K,which meets the imaging requirements.Subsequently,the radiometer was used to build a terahertz passive imaging system,and the imaging effect was excellent,thus verifying the good performance of the terahertz passive imaging front end.