Variable-Frequency Microwave Cavity Spectrometer

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Abstract
A variable‐frequency, resonant cavity spectrometer was developed for the investigation of molecular gases in the 10‐cm spectral region. Either Stark or Zeeman modulation could be applied. A single coaxial cavity, operated in the TEM mode, served as the Stark or Zeeman modulation cell and as the frequency tuning and stabilizing mechanism. The rf power transmitted through the cavity was detected by a bolometer and the signal component at the fundamental modulation frequency amplified and passed to a phase sensitive detector. The minimum detectable absorption coefficient for the spectrometer was determined to be αmin = 1×10−10 cm−1.