Directive Diagrams of Antenna Arrays 



By RONALD M. FOSTER 



Synopsis: Two syslenialic cuUeclions of directive amplitude diagrams 

 are shown for arrays of 2 and of 16 identical antennae spaced at equal dis- 

 tances along a straight line with equal phase differences introduced between 

 the currents in adjacent antennae, assuming that each antenna radiates 

 equally in all directions in the plane of the diagram. Three diagrams show 

 the effect of increasing without limit the number of antennae in a given 

 interval. Two models show the effect of distributing the antennae over 

 an area. 



Introduction 



ONE of the means proposed for obtaining directive radio effects, 

 both in sending and in receiving, is the antenna array, consisting 

 of a system of two or more antennae situated at specified fractions 

 of a wave-length apart and with relations imposed upon the ampli- 

 tudes and phases of the currents in the several antennae. For example, 

 consider a sending array consisting of two vertical antennae so ar- 

 ranged that the currents in the antennae are equal in magnitude but 

 a half period apart in phase, the individual antennae being identical 

 and radiating equally in all directions in the horizontal plane. If 

 the two antennae were placed at the same point there would be zero 

 transmission in all directions, since the effects of the two antennae 

 would neutralize each other. If, however, the two antennae are 

 separated by a small fraction of a wave-length, while there will still 

 be zero transmission in the direction perpendicular to the axis of the 

 array, there will be transmission in all other directions. If this 

 separation is increased to exactly one-half of a wave-length, the 

 radiation from the array along the axis will become a maximum. 



This particular type of antenna array was proposed by Brown ^ 

 in 1899. A few years later, Stone ^ proposed a similar array with 

 the two currents exactly in phase. This array gives maximum trans- 

 mission perpendicular to the axis, zero transmission along the axis. 

 About the same time, Blondel ^ made several suggestions, among 

 them, two antennae placed a quarter of a wave-length apart and 

 with a phase difference of a quarter of a period. With this arrange- 

 ment a unilateral effect is obtained, there being maximum trans- 

 mission in one direction along the axis, zero transmission in the op- 

 posite direction. 



IS. G. Brown, British Patent No. 14,449 (1899). 



2 J. S. Stone, United States Patent No. 716,134 (1901). 



3 A. Blondel, Belgian Patent No. 163,516 (1902), British Patent No. 11,427 (1903). 



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