Selective Fading of Microwaves

During the past few years, studies of microwave propagation have been made by the Radio Research group at the Holmdel Laboratory over two paths located in eastern New Jersey. Both of these are lineof-sight paths which might be considered to be typical links in a crosscountry microwave radio relay circuit. In conducting these studies, the usual continuous recordings of signal levels were made but the greater interest was centered in special experiments designed to reveal more of the processes which can cause fading. The most relevant information has been obtained by exploring the incident wavefronts with a narrow-beam scanning antenna (angle-of-arrival studies) and, more recently, by observing the transmission characteristics of the paths by means of a frequency-sweep technique and also by the use of very short pulses. Some results of angle-of-arrival observations have been reported previously 1 and a companion paper describes the transmission tests conducted with very short pulses.2 The present paper describes some of the observed mechanisms associated with fading, presents typical data obtained with the narrow-beam scanning antenna and gives examples of the frequency-sweep observations, illustrating the frequency selective 1 W. M. Sharpless, "Measurement of the Angle of Arrival of Microwaves," Proc. I.R.E., 34, Nov. 1946, pp. S37-845. A. B. Crawford and W. M. Sharpless, " F u r t h e r Observations of the Angle of Arrival of Microwaves," Proc. I.R.E., 34, Nov. 1946, pp. 845-848.