Superior Impedance Matching of THz Antennas with HTSC Josephson Junctions

A bow-tie antenna with a step-edge Josephson junction as the detection element, located at the center of the antenna, was investigated. The performance of these detection systems is highly sensitive to impedance mismatch between the antenna and the Josephson junction. Impedance matching optimization was performed using advance microwave simulations. Based on simulations results a bow-tie antenna system was implemented and analyzed. Following our experimental results, in the presence of a 200 GHz RF signal, and further simulations, we developed an improved structure where the junction is placed between the ends of two matching strips rather than in center of the antenna. This configuration was analyzed for two antenna structures: bow-tie and planar wire dipole. We found that the dimensions of the matching strips affect both detection magnitude and frequency of return loss dip, and that reflection is extremely sensitive to the junction length. The reflectivity obtained for an antenna without a matching unit was around −14 dB while for an antenna with a matching unit return loss up to −35 dB was derived. Simulation results also showed a high directivity of the antenna, with high radiation gain and low return loss. By varying antenna and junction dimensions, we derived an optimal design in the range of 200–280 GHz.