An improved version of a microwave spectrometer operating in the vicinity of 70 GHz is described. The spectrometer, which incorporates a Fabry-Perot resonator and-superheterodyne detection for high sensitivity is designed for the detection of gaseous pollutants and other atmospheric constituents. The instrument is capable of detecting polar molecules with absorption coefficients

A new version of a microwave spectrometer for the detection of gaseous pollutants and other atmospheric constituents is described. The spectro meter, which operates in the vicinity of 70 GHz, employs a Fabry-Perot resonator as a sample cell and uses superhetrodyne detection for high sensitivity. The spectrometer has been modified to incorporate a frequency doubler modulated at 30 MHz to permit operation with a single Gunn oscillator source. As a result, faster response time and somewhat greater sensitivity is obtained. The spectrometer is capable of detecting a minimum concentration of 1 ppm of S0~ diluted in air with a 1 second time constant. For OCS diluted in air, the minimum detectable concentration is 800 ppb and with a 10 second time constant 300 ppb.