An Experiment on Propagation of 60-GHz Waves Through Rain

Crowding of the frequency spectrum is forcing designers of microwave communication systems to use higher frequencies and to give serious consideration to orthogonally polarized waves for increasing communication capacity. If adequate orthogonality can be maintained, the capacity of a system is double that of a system employing only one polarization. However, it has long been known that imperfections in antennas and other system components limit the degree of orthogonality that can be maintained in a practical system. Rainfall on the transmission path can also affect polarization and thereby limit the degree of discrimination against the unwanted signals at the receiver. The experiment described here was set up to determine the extent of such depolarization as well as the attentuation of 60-GHz waves. The mechanism of attenuation and depolarization involves the geometry of raindrops. A number of workers have determined that large raindrops are seldom spherical and that they arc capable of producing different amounts of attenuation for waves having different polarizations. 1,2 At the time our experiment was in the design stage, 165