Design and performance of flux-flow type Josephson oscillator coupled to a stripline

In order to realize efficient coupling between a flux-flow type Josephson oscillator (FFO) and an external stripline, the authors carried out experiments to investigate the inductive coupling scheme in a strong coupling regime. By adopting NbN films with large penetration depths as electrodes for strong coupling, they were able to realize coupling sections with a coupling coefficient α=M/√ L₁L₂ as large as 0.7, with M , L₁, and L₂ being mutual inductance, self-inductances of, the FFO, and the stripline, respectively. Using this design for the coupling, the authors succeeded in detecting AC fields at frequencies around 150 GHz, which were emitted from FFO to the stripline via the coupling section