64 BELL SYSTEM TECHNICAL JOURNAL 



waves rather than short waves, thereby deferring many of the appHca- 

 tions of these suggestions. 



The principle of wave interference on which most short-wave 

 systems of directive radio are based has probably been known for 

 several centuries. However, the first thorough treatment of this 

 subject was by Sir Thomas Young, ^ who, together with Fresnel, 

 securely established the wave theory of light in the early part of the 

 last century. Even Hooke and Huygens, who had offered the wave 

 theory over a century earlier, failed to recognize the full significance 

 of interference. 



When Hertz started his celebrated experiments to verify Maxwell's 

 theory he was, of course, in full knowledge of these phenomena and 

 their explanation, and invoked their use in proving the existence of 

 electric waves. It is interesting that in some of his experiments he 

 made use of parabolic mirrors for both transmitting and receiving, 

 having directional characteristics very similar to those sometimes 

 used in present day radio practice. It is also of interest that he found 

 that parallel wires stretched over a frame were quite as eff^ective as a 

 reflector as a continuous sheet of metal of similar dimensions, pro- 

 vided the wires were kept parallel to the lines of electric force of the 

 arriving wave. He apparently did not in\estigate the effect of varying 

 the spacing nor the length of the parallel wires, nor did his subsequent 

 experiments otherwise tend toward the present day antenna array 

 technique. 



This paper treats in an elementary way certain aspects of the 

 antenna array problem, principally as regards the manner in which 

 calculated directivity is affected by the number and spacing of the 

 individual antennas which go to make up the array. The theory is 

 applicable only to those forms of directive antennas which may be 

 resolved into a series of individual sources. It does not apply to the 

 so-called wave antenna. However, principles are included which have 

 for some time been in general use in combining two or more such 

 antennas. 



Extensive study has been given to directive antenna systems for 

 use in transoceanic radiotelephony. Papers dealing with this general 

 subject have appeared from time to time.' F'urther work is in prog- 

 ress. Papers by E. J. Sterba and also by E. E. Bruce and H. T. Friis of 

 the Bell Telephone Laboratories are in preparation which will include 



1 Phil. Trans, of Royal Soc, 92, 12; 1802. 



^ R. M. Foster, "Directive diagrams of antenna arrays," Bell Sys. Tech. Jour., 

 292, May, 1926. Austin Bailey, S. W. Dean, and \V. T. Wintringham, "Receiving 

 system for long- wave transatlantic radiotelephony, Proc. I. R. E., 16, 1694, December, 

 1928. J. C. Schelleng, "Some problems in short-wave radiotelephone transmission," 

 Proc. I. R. E., 18, 913; June, 1930. 



