66 BELL SYSTEM TECHNICAL JOURNAL 



side the scope of this paper. However, bibliographies are cited below 

 covering some of their important phases. 



Elementary Principles 



The interference patterns resulting from a number of individual 

 sources of waves, such as antennas, are dependent on both their 

 spacial arrangement and the magnitudes and relative phases of their 

 forces. This makes possible an almost unlimited number of com- 

 binations of which only a portion have thus far found use in com- 



(a) 



Fig. 2 — Interference pattern. Two sources separated in space by one-fourth wave- 

 length and in time by one-fourth period. 



munication. This paper will restrict itself mainly to some cases which 

 are already finding general application. As a suitable introduction 

 to this subject, a very simple case of wave interference is discussed in 

 the following paragraph. 



Figs, la and 2a depict in a rough way the interference resulting 

 from two independent sources of spherical waves of the same ampli- 

 tude. In the first case they are spaced ^ wave-length but are assumed 

 to be oscillating in phase. In the second case the two sources are sepa- 

 rated in space by 3^ wave-length and in phase by ]i period. Crests 



