Most reliable messenger - MM-waves get through

The four classes of environmental phenomena that significantly affect the efficiency of terrestrial millimeter-wave technology are molecular resonance, airborne particulates, tropospheric thermodynamics, and terrestrial path modifiers. Each of these is discussed. Reflector antennas are then compared with horn-fed antennas, and the latter are shown to be better suited. In addition to their other advantages, scalar horns have (1) nearly identical radiation patterns in all axial planes; (2) almost constant beam widths over wide bandwidths; (3) extremely small side- and back-lobes; and (4) a true fixed phase center coincident in both the E- and H-planes. For millimeter-wave communication links in the 50-to-70-GHz regions, rain-induced attenuation can be mitigated by judicious frequency selection together with adaptive frequency control. However, energy scattering caused by rain and the variable character of rainfall conflict with low-probability-of-intercept objectives.