@misc{indiciaeabfb3db3c037,
  title = {The classical microwave frequency standards},
  author = {Busca, Giovanni and Thomann, Pierre and Laurent-Guy, Bernier and Willemin, Philippe and Schweda, Hartmut S.},
  year = {1990},
  url = {https://ntrs.nasa.gov/citations/19910016443},
  note = {Source identifier: 19910016443}
}