Selectively Faded Nondiversity and Space Diversity Narrowband Microwave Radio Channels

(i) During periods of multipath propagation on line-of-sight radio links, deep and selective fading can severely corrupt the desired uniform transmission characteristics of a narrowband microwave channel received on a single antenna. Fortunately, because the multipath processes are sensitive functions of space, 1 the likelihood of simultaneously encountering both deep and frequency-selective fading on two vertically spaced antennas is very small. Earlier studies 2 were directed toward quantification of the spectral and temporal behavior of the amplitude distortion occurring in a nondiversity narrowband radio channel derived from a single receiving antenna. In the present paper, we describe a second experiment undertaken in 1971 to extend the 239 240 T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , F E B R U A R Y 1 9 7 3 nondiversity measurements and to examine the amplitude distortions occurring in a diversity channel derived from the narrowband signals received on a pair of vertically spaced antennas. The data used in this analysis were taken between June 16 and September 16, 1971 (93 daj^s), and included the amplitude measurement of 62 uniformly spaced, coherent tones spanning 33.55 MHz at 6 GHz transmitted over a 26.4-mile radio path and received on two antennas of vertical separation of 19 feet 3 inches. The tone fields received on the two antennas were sampled five times per second and the results recorded whenever significant amplitude activity was occurring anywhere in cither channel.