A Study of Frequency Selective Fading for a Microwave Line-of-Sight Narrowband Radio Channel

The spectral and temporal characteristics of a narrowband radio channel subject to multipath fading were estimated from a detailed sampling of channel loss variations. The data base for this characterization was obtained during a 59-day experiment in which the amplitudes of a set of coherent tones spanning a band of 33.55 MHz and centered at 6034.2 MHz were continuously monitored. The more significant observations were: (i) For fade depths less than 30 dB the frequency selectivity is accurately described by linear and quadratic components (in frequency) of amplitude distortion. The derived statistical distributions of such distortion parameters exhibit slopes of a decade of decrease in probability of occurrence for each 10 dB increase in distortion, for bandwidths greater than 5 MHz. (ii) For fade depths greater than 30 dB and bandwidths in excess of 5 MHz the amplitude distortion exceeds second order. (iii) Maximum observed rates of change for the linear and quadratic distortion were 90 and 60 dB/second, respectively.