Millimeter-wave sensitivity of YBCO grain boundary Josephson junctions coupled with coplanar waveguide-fed slot dipole antennas

Improvements in the coupling efficiency of millimeter wave quasioptically introduced to high-T_C Josephson junction detectors have been studied. Both increasing of junction resistance and implementation of a lower impedance antenna are required to improve the efficiency. We designed a coplanar waveguide feed slot dipole antenna as a low impedance antenna combined with the Josephson junction detectors. Improvements in the coupling efficiency due to decreasing of antenna impedance have been demonstrated and compared with numerically obtained results by the finite difference time domain method on the slot dipole antenna.