| Atmospheric transmission characteristics of terahertz waves in the vicinity of 440,550,620,730,870 GHz exists relatively transparent window, so it is really important to do some research on these particular frequency. In most of THz communication and radar systems, the mixer is the first stage in the receiving system because of the lack of low-noise amplifier. Therefore, the performance of the mixer is directly related to the entire receiving system. Due to the difficulty in achieving oscillation source, reducing the frequency of the local oscillator to half of its original frequency which is the sub-harmonic mixer is the best solution. Therefore, the design of 440 GHz sub-harmonic mixer becomes a very important task.First of all, this paper introduced the development of THz sub-harmonic mixer in recent years, then we did some research on the characteristics of the Schottky diode and mixing theory. Based on the mixing thesis, we simulated and modelized the Schottky diodes, after that we can get the port data by extracting package model, therefore, we can bring the design of schottky diodes into the whole circuit. This paper started with the three-dimensional electromagnetic analysis of the 440 GHz sub-harmonic mixer. With the use of the Schottky diode made by China Electronics Technology Group Corporation-13 Institution and 50μm quartz substrate, simulation results show that in the 420-460 GHz conversion loss is less than 8dB. Due to the small size of the circuit, machining accuracy have become a big problem. 440 GHz sub-harmonic mixer tolerance analysis carried out in order to minimize processing errors that may arise. Finally, this paper did some research on testing the 440 GHz sub-harmonic mixer. Result shows that conversion loss is about 20-30 dB during 420-430 GHz, the optimal frequency conversion loss is 17 dB in 430.56 GHz.The research provides a good technical and theoretical basis for higher frequency sub-harmonic mixer research work in the future. |
