A dual Wi-Fi antenna is a pair of identical antennas on a wireless router or Wi-Fi-equipped device, intended to eliminate signal fading and dead spots. Dual Wi-Fi antennas operate on a principle known as antenna diversity, which offers two different reference points for signal reception or transmission (or both) and uses the better one. These systems all operate on the principle of antenna diversity, which engineers have exploited in long-distance communications systems for decades.
When a Wi-Fi device operates in an indoor environment, the electromagnetic waves (radio-frequency signals) reflect from various metallic objects such as electrical wires, steel beams, and household appliances. The signal arriving at the receiving end of the circuit therefore comprises several different component waves that rarely, if ever, perfectly reinforce each other. At certain points in space, the components effectively cancel each other out, producing dead spots. (This effect can occur even if the router and the end-user device lie on a direct line of sight but far away from each other, because reflected signal components inevitably exist in addition to the line-of-sight signal.) If both devices have single antennas, the user can experience considerable frustration. In severe cases, a drop-out (and consequently a lost connection) can occur even if the user moves by only a few centimeters, or changes the angle in which the device is held.
A dual antenna on either the router or the end user device offers a solution to the problem of Wi-Fi fading, dead spots, and drop-outs. If one of the antennas falls into a dead spot, the device can switch to the other antenna, which will most likely provide a usable signal. The Wi-Fi system constantly monitors the signals from both antennas and automatically uses the stronger of the two. A dual Wi-Fi antenna requires additional hardware and integration compared with a single antenna, but many users find that the performance improvement justifies the increase in complexity and cost.