| In recent years, researches on superconducting electronics and its applications have undergone rapid development. A series of superconducting electronic devices based on Josephson effect and Flux quantum effect, including SQUID, mixer, detector, generator, amplifier, voltage standard and superconducting digital circuit, have been developed. Due to their inherent advantages, such as:low noise, low power consumption, high sensitivity, rapid response and broad bandwidth, these devices have been applied in many areas, e.g. military, aerospace, medicine, etc. In this dissertation, high frequency characteristics of high-temperature superconducting Josephson junctions and their related applications were investigated systematically through simulations and experiments. The main research contents and results are listed as follow:1. An 8mm waveband semi-confocal Fabry-Perot resonator designed by using the CST microwave studio software was produced. Employing this resonator, a set of characteristics measurement system for high-temperature superconducting Josephson junctions was developed. This system has several characteristics as follow:Firstly, the Fabry-Perot resonator can resonate in TEMooq mode by carefully adjusting the distance between the two mirrors of the resonator. When it works in TEM mode, the electromagnetic field distribution near the plane mirror is similar to the plane wave. It can irradiate uniform power on the Josephson junction arrays. Secondly, the position of the sample can be adjusted finely to locate the sample in a position with strong electric field. Thirdly, the direction of electric field relative to the sample can be changed conveniently. Consequently, an optimum coupling between external electromagnetic fields and the sample can be obtained through adjusting the Fabry-Perot resonator, and thus high quality Shapiro steps can be expected to observed, which is useful and significant for applications of Josephson junctions in voltage standard, mm and sub-mm wave detection and radiation, etc. 2. Characteristics of Tl2Ba2CaCu2O8 (Tl-2212) bicrystal Josephson junctions are explored experimentally. Despite of deep investigations on the characteristics of high-temperature superconducting Josephson junctions, researches based on Tl-2212 superconducting thin films are deficient compared with YBCO thin films, especially on SrTiO3 (STO) substrates. Since Tl-based thin films have the merits of higher transition temperature and higher resistance to moisture, they are more suitable for microwave applications. In particular, our researches are based on STO substrates which, generally speaking, are not suitable for high frequency applications for their high dielectric constant and dissipation factor, however, according to our experiment results, vertical and high amplitude Shapiro steps can also be observed from bicrystal Josephson junctions fabricated on STO substrates when they are irradiated by external microwave.3. The characteristics of mm-wave emission from YBCO high-temperature superconducting bicrystal Josephson junction array were measured experimentally. The research results show that the impedance matching between one junction and external microwave circuits is hard to realize because of the very small impedance of one junction, and thus the radiation from one junction is very weak and of no practical use. Then how to increase the radiation power? We adopted a series of techniques to circumvent this problem, including:employing series-connected Josephson junctions, integrating half-wavelength dipole array, using the substrates as a dielectric resonator and making it resonate together with the Fabry-Perot resonator.4. Taking advantage of Tl-2212 thin film epitaxially grown on 20°tilted LaA103 substrate, we fabricated intrinsic Josephson junction array. Both multiple branches and single branch of the I-V characteristics (IVC) were observed. The IVC showed very strong hysteresis which proved that our intrinsic junctions are SIS type. The multiple branches are caused by ununiformity of the size of the intrinsic junctions in an array. After improving the etching process, one single branch IVC can be observed. Putting the intrinsic junctions in the Fabry-Perot resonator and performing measurements of millimeter-wave irradiation characteristics, no Shapiro steps were observed, yet we found that the external microwave had a very strong influence on the intrinsic junctions. Just irradiated by a lOmW microwave power, the critical current of the intrinsic junction array was suppressed to zero, which proved that the coupling between the external microwave and the intrinsic junctions is improved efficiently. The research results are very useful and significant for applying intrinsic junctions in high frequency sources.
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