You may have seen some wireless routers having two antennas that are identical. If you wonder why some Wi-Fi-equipped devices have a pair of antennas, then here is the reason behind it. Dual antennas are generally affixed at two nearby reference points for antenna diversity. This means that there would be two points of signal transmission or reception and you would be able to make use of the better one out of them. You receive a signal from the reference point that offers better signal strength at a specific wavelength.
