The antenna elements can be arranged to form a 1 or 2 dimensional antenna array. A number of antenna array specific aspects will be outlined; we used 1dimensional arrays for simplicity reasons. Antennas exhibit a specific radiation pattern. The overall radiation pattern changes when several antenna elements are combined in an array. This is due to the so called array factor: this factor quantifies the effect of combining radiating elements in an array without the element specific radiation pattern taken into account. The overall radiation pattern of an array is determined by this array factor combined with the radiation pattern of the antenna element. The overall radiation pattern results in a certain direction and thus gain linked through the efficiency with the direction. Direction and gain are equal if the efficiency is 100%.
Broadside vs. end fire arrays
Arrays can be designed to radiate in either broadside i.e. radiation perpendicular to array orientation (the z axis in figure 1) or end fire i.e. radiation in the same direction as the array orientation (the y axis in figure 1). We will focus on broadside arrays and only radiation in the z direction is considered. This allows for easy transformation to 2dimensional planar arrays with the elements in the xy plane. For linear arrays the radiation patterns given below are a cross section in the yz plane. Actually, the 3dimensional radiation pattern of a linear array is a rotation around the y axis of the patterns given.
Feed network of the array
The individual antenna elements in an array are fed using a feed network. The complexity of the feed network depends on the number of elements, the amplitude and/or phase distribution between the elements, the ability to do beam steering… It is important to realize that the feed network is the most complex part of the array