342 



BELL SYSTEM TECHNICAL JOURNAL 



known that multiple Ionosphere reflections usually produce several 

 more or less discrete waves, or bundles of waves, having diff^erent 

 vertical angles and diff^erent transmission delays. To obtain the 

 maximum advantage, however, requires that all of the several wave 

 bundles be separately received and suitably combined after the trans- 

 mission delays have been equalized. The achievement of this objective 



Fig. 2 — ^Airplane view of the three-quarter-mile experimental MUSA on the re- 

 ceiving laboratory site located near Holmdel, New Jersey. The white line beneath 

 the antennas is the newly filled trench in which coaxial transmission lines are buried. 

 The building appearing in the right-hand foreground houses the receiving apparatus. 

 The ground is flat to within ± 4 feet. 



not only yields the ultimate gain in signal-to-noise ratio but at the 

 same time reduces the distortion associated with selective fading. 



The method of obtaining sharp steerable directivity by combining 

 the output of fixed antennas through phase shifters makes it possible 

 to use the same antennas and transmission lines to provide several 

 separately steerable lobes each of which is in effect an independent 

 MUSA.^° In the experimental system, shown schematically in Fig. 3, 



1" R. K. Potter, U. S. Patent No. 2,030,181. 



