GAIN OF DIRECTIVE ANTENNAS 



65 



certain calculated data similar to those contained in the present paper, 

 and also experimental results obtained from tests on actual antennas of 

 various sizes and proportions. 



In the early part of the following discussion each antenna is con- 

 sidered as a spherical source of waves which radiates equal power in 

 all directions. Furthermore, it assumes that the current in each 



(a) 



Fig. 1— Interference pattern. Two equiphased sources spaced one-half wave-length. 



individual source, in a given array, is the same and is not materially 

 affected in either magnitude or phase by its proximity to other sources. 

 The fair approximation to which these calculated results are realized 

 in practice bespeaks the justification of these assumptions. 



The various steps by which present day directional radio has been 

 developed are extremely interesting, but they are so involved in the 

 development of radio itself that their enumeration is considered out- 



