Microwave Line-of-Sight Propagation With and Without Frequency Diversity

Line-of-sight microwave systems are affected by multipath propagation. When this phenomenon is present, the output from a receiving antenna can be practically zero for seconds at a time. Experimental data are difficult to obtain because long time periods of continuous coverage are needed to observe sufficient fading activity at the fade depths (3040 dB) of interest for high performance systems. The literature is extensive on this general topic1 7 but limited and in some cases contradictory8 for these fade depths. The results available regarding frequency diversity are even more limited0. For these and other reasons, an extensive experimental program was undertaken in 1966. 1827 1828 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1970 Continuous amplitude measurements were made for 68 days at a rate of 5 samples per second per channel for seven 4-GHz and six 6-GHz signals on a radio relay path at West Unity, Ohio. Identical measurements were also made for one 4-GHz signal on a second path having a common reception point with the first path. Here a 68-day summer period (July 22 to September 28) in 1966 has been subjected to detailed analysis. We present the results of the data analysis and their interpretation along with pertinent background information. Briefly the order of presentation is (i) experiment description, (ii) determination of the reference values used for calibration, (Hi) nondiversity results, (iv) frequency diversity results, (v) a mathematical description of pairwise fading which is used to interpret the improvement obtained from frequency diversity, (vi) 4/6 GHz crossband results, (vii) adjacent hop results, and (viii) a comparison of space and frequency diversity.