Anomalous and near-zero group-velocity dispersion in the sub-THz and mm-band atmospheric windows

Analysis of the complex refractive index of atmospheric air reveals remarkably broad and continuous regions of anomalous and near-zero group-velocity dispersion in the subterahertz (sub-THz) and millimeter-band atmospheric windows. One such broadband dispersion anomaly is shown to occur in the high-frequency wing of the 60-GHz band of molecular oxygen. Adjacent to this dispersion anomaly is a broadband atmospheric transparency region within which the group-velocity dispersion is unusually weak, enabling distortion-free long-distance transmission of broadband millimeter-wave field waveforms, as well as broadband remote sensing in the millimeter band. Although broad regions of anomalous and near-zero dispersion also exist in the sub-THz range, their utility for long-distance transmission and remote sensing is limited because of strong atmospheric absorption.