Rapid-Scanning Fourier Transform Spectrometer for Studies of Propagation of Near-Millimeter-Wave Radiation through Clear Air and Fog

摘要

A system has been developed to measure relative atmospheric transmission for the near-millimeter wave range of frequencies, 60-100 GHz. A 400 m long propagation range has been established. A transmitter/receiver system at one end of a link incorporates a rapid-scanning Fourier transform spectrometer. It involves a novel mirror drive which moves both interferometer mirrors simultaneously. The interferometric section is a polarizing Martin-Puplett type. The grid polarizers are made photolithographically. The source is a hot mercury lamp in a cavity, and the detector, an InSb photoconductive element. Scans of 7.5 GHz resolution require about 0.2 sec. A dihedral retroreflector 200 m from the transmitter/receiver reflects the signal back and completes the link. Calibration spectra are obtained from a short path to a second retroreflector. System tests are described.