Superconductor filter device and manufacturing method thereof

A superconductor filter is stored in a hermetic filter case so that electrical connection can be provided between the superconductor filter and the outside of the hermetic filter case. The hermetic filter case is stored in a hermetic outer case so that electrical connection can be provided between the superconductor filter and the outside of the hermetic outer case and so that air/gas flow through pipes can be implemented between the inside of the hermetic filter case and the outside of the hermetic outer case. The hermetic filter case and the hermetic outer case are evacuated into vacuum, and the superconductor filter is cooled below its critical temperature. After the superconducting state of the superconductor filter could be observed, gas that does not deteriorate or react with the superconductor filter is gradually packed in the hermetic filter case and thereby the dielectric constant around the superconductor filter is raised from the dielectric constant of vacuum. The amount of the gas packed in the hermetic filter case is increased/decreased while observing transmission characteristics (center frequency etc.) of the superconductor filter, until desired transmission characteristics are obtained. Thereafter, the hermetic filter case is hermetically sealed so that the amount of the gas in the hermetic filter case will thereafter be fixed.