Terahertz Characterization of External Resonant Systems by High- $T_{c}$ Josephson Junctions

High-Tc Josephson technology looks promising for THz applications. One of the remaining problems, important both for detection and emission of THz radiation, is an optimum coupling of high-Tc junctions with environment. Recently, we have demonstrated a possibility to characterize electromagnetic systems integrated with high-Tc junctions using dc I-V curves of these junctions. Here, we report in details on modification of the dc I-V curves of YBa₂Cu₃O_7-x bicrystal junctions, related to interaction of Josephson oscillations with terahertz resonance antennas. Thin-film log-periodic antennas with various resonance structures were fabricated on the same substrate as Josephson junctions and were excited by Josephson oscillations. Frequency-dependent admittances of the antennas were derived from fine log-periodic structures on the dc I-V curves of the junctions and compared with the results of numerical simulations. Data obtained can be used for optimization of coupling between the junctions and antennas.