Directive Diagrams of Antenna Arrays

TWO systematic collections of directive amplitude diagrams are shown for arrays of 2 and of 16 identical antennae spaced at equal distances 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 O NE 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 amplitudes and phases of the currents in the several antennae. For example, consider a sending array consisting of two vertical antennae so arranged 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.