Introduction to Antenna Arrays

An antenna array is a set of N spatially separated antennas. The number of antennas in an array can be as small as 2, or as large as several thousand (as in the AN/FPS-85 Phased Array Radar Facility operated by U. S. Air Force). In general, the performance of an antenna array (for whatever application it is being used) increases with the number of antennas (elements) in the array; the drawback of course is the increased cost, size, and complexity. The following figures show some examples of antenna arrays. Figure 1. Four-element microstrip antenna array. Figure 2. Cell-tower array. These are typically used in groups of 3 (2 receive antennas and 1 transmit antenna). The general form of an array can be illustrated as in Figure 3. An origin and coordinate system are selected, and then the N elements are positioned, each at location given by: The positions are illustrated in the following Figure. Figure 3. Geometry of an arbitrary N element antenna array. Let represent the output from antennas 1 thru N, respectively. The output from these antennas are most often multiplied by a set of N weights - - and added together as shown in Figure 4. Figure 4. Weighting and summing of signals from the antennas to form the output. The output of an antenna array can be written succinctly as: This is what is going on in an antenna array. However, I haven't answered what the benefits of doing this are. To understand what happens in an antenna array, click the next link.