Antenna Arrays: A Computational Approach

1 Antenna Array Basics

Big antennas can detect faint signals much better than small antennas. A big antenna collects a lot of electromagnetic waves just like a big bucket collects a lot of rain. The largest single aperture antenna in the world is the Arecibo Radio Telescope in Puerto Rico (Figure 1.1). It is 305 m wide and was build inside a giant sinkhole. Mechanically moving this reflector is out of the question.

Another approach to collecting a lot of rain is to use many buckets rather than one large one. The advantage is that the buckets can be easily carried one at a time. Collecting electromagnetic waves works in a similar manner. Many antennas can also be used to collect electromagnetic waves. If the output from these antennas is combined to enhance the total received signal, then the antenna is known as an array. An array can be made extremely large as shown by the Square Kilometer Array radio telescope concept shown in Figure 1.2. This array has an aperture that far exceeds any antenna ever built (hundreds of times larger than Arecibo). It will be capable of detecting extremely faint signals from far away objects.

An antenna array is much more complicated than a system of buckets to collect rain. Collecting N buckets of rain water and emptying them into a large bucket results in a volume of water equal to the sum of the volumes of the N buckets (assuming that none is spilled). Since electromagnetic waves have a phase in addition to an amplitude, they must be combined ...