We have seen in the discussion of the radiated fields of wire and aperture antennas that the radiated fields consist of contributions from an infinite number of elementary sources. On a macroscopic level, we may group elementary sources into antenna elements and then use these antenna elements to create a larger aperture antenna. The benefits of such an operation are twofold. First an aperture antenna is created occupying a relatively small volume allowing control over the field distribution. Second, by applying a phase-taper over the elements that make up the aperture, the radiated beam may be pointed into a desired direction without physically moving the antenna. Although array antennas come in many forms, including linear, planar, curved and three-dimensional ones, we will only discuss array antenna basics and therefore will stick to the linear array antenna.1
8.1 A Linear Array of Non-Isotropic Point-Source Radiators
Let's assume a system of identical radiators, placed at equidistant positions along a straight line, see Figure 8.1. This system is a so-called linear array antenna. Neither the identicalness of the radiators, nor their equidistant positions are prerequisites for a linear array antenna. They are introduced though to avoid obscuring the explanation of the linear array antenna basics. Besides, in practical situations, linear array antennas are often realized with identical radiators that are equidistantly positioned.