Hts Bi-crystal Junction Mixers Noise Figure Analysis At THz Band

High temperature superconducting (HTS)Josephson bi-crystal Junction has highly nonlinear and THz response characteristics, the signal mixing detector system constituted by HTS Josephson junction has many unique advantages including high sensitivity, wide response frequency band, high frequency conversion efficiency, low noise figure and so on. High performance HTS bi-crystal Junction has been successfully fabricated in this thesis.We have measured the harmonic frequency mixing and realized the weak signal detection at the THz frequency band. The frequency conversion efficiency and noise figure characteristics are important parameters of HTS bi-crystal Junction mixers for application, noise figure is an important indicator for the measurement of mixer’s internal noise and the influence of its sensitivity. The HTS bi-crystal Junction harmonic mixers and noise figure automatic measurement system are built.We have researched and analyzed the HTS harmonic mixing detector’s frequency conversion efficiency, noise figure at THz frequency band measurement and data analysis. The research work carried out and the results are as follows:1. YBCO/YSZ, YBCO/MgO, TIBCCO/MgO Josephson junctions have been fabricated through argon ion band etching. Through improving the bi-crystal junction manufacture technology, we have successfully fabricated the Josephson junctions with characteristic voltage of1mV, which have very good microwave response at210GHz and650GHz. At the same time we simulate Josephson equivalent circuit characteristics by Matlab program, from the numerical calculation to further more understanding the theory of the Josephson Effect and microwave characteristics. 2. Through the experiment and measurement of the HTS bi-crystal mixer’s harmonic frequency mixing and noise figure, we have demonstrated the relationship between the frequency conversion efficiency with harmonic number, bias current, the LO power and the noise figure with bias current, the LO frequency. The mixer noise figure of about lOdB around100GHz and13dB around210GHz has been measured using Y-factor method. This provides an important basis for the low-noise HTS mixer systems in the high harmonic mixer, and other highly sensitive detection system3. Using IRIRE KOKEN company production GC70K, we build the measurement system by the small pulse tube refrigerator and measuring instruments and collect the data by automatic measurement programming system. This real-time detection measurement system lays the foundation for the establishment of small, modular, digital, automated measurement system.4. In order to strengthen the coupling of bi-crystal Josephson junction and the THz signal, we use the quasi-optical systems. According to the antenna simulation analysis by HFSS program, we also design the LPDC antenna corresponding THz source frequency band to improve signal coupling and the bi-crystal junction frequency mixing performance.This thesis’s research work provides an important research foundation and the key parameters for THz signal detection and its application by the HTS Josephson mixer detector.