The dBi rating for a Wi-Fi antenna compares its performance to an isotropic antenna. If the isotropic antenna produces 1 milliwatt of radio wave power and the Wi-Fi antenna produces 2 milliwatts, that is 10 * log(2) or 3 dBi. If another antenna produces 3 milliwatts, that is 10 * log(3) or 4.8 dBi. Though the isotropic antenna doesn’t exist, it still serves as a reliable way to compare Wi-Fi antennas. You can compare the dBi ratings of the two antennas and choose one with the better dBi rating.
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