188 



BELL SYSTEM TECHNICAL JOURNAL 



ceived field strength since the half wavelength path difference plus the 180- 

 degree phase change at reflection causes the direct wave and the reflected 

 wave to arrive in phase at the receiver. In Fig. 1-4, the first Fresnel region 

 is sketched on the profile map of a typical microwave link for wavelengths 

 of 3 meters and 3 centimeters. 



It should be emphasized that the above remarks on ground reflections 

 apply only for rough terrain and for the case of reflection at a distance from 







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60 70 80 10 20 

 ANTENNA HEIGHT IN FEET 



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Fig. 1-3. — Variable antenna-height tests on several of the New York-Boston 

 repeater circuits. X = 7 cm. 



the terminals. Variable height experiments involving short distances over 

 open flat fields reveal the presence of almost perfect ground reflections at 

 wavelengths as short as 1.25 centimeters. For transmission paths over 

 water, strongly reflected components are often observed. Reports' of 

 experiments in the Arizona desert indicate a strong ground reflection at 

 wavelength of 3 centimeters. In such locations, and most likely in the 

 plains regions, the presence of substantial ground reflected components may 

 prove to be troublesome. 



» Report No. 6. Electrical Engineering Research Laboratory, The University of Texas, 

 February 1, 1947. 



