Using antenna arrays for diversity reception is one of the most straightforward uses of antenna
arrays. Because the power level of a received signal can vary significantly with small changes in
distance, a diversity array simply uses a set of antennas and combines the signals to obtain the maximum
signal. Consider the example of Figure 1. Someone is talking on their cell phone, and a hypothetical
(though reasonable) power is shown in the areas around the user.|
Figure 1. Example of signal level versus position.
To combat this effect (known as fading), an array of antennas can be used. For instance, if 3 antennas are placed in the above situation, as shown in Figure 2, the antenna with the maximum signal can be selected and used.
Figure 2. Three antennas used in a diversity array.
Finally, diversity reception can occur for two antennas not separated, but receiving orthogonal polarizations. If one antenna receives vertically polarized waves, a second antenna can be placed near the first that receives horizontally polarized waves (which in a fading environment, are not strongly correlated). In this manner, diversity can be achieved.
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