Why does the FCC allow higher output power transmissions when using beam forming techniques?
FCC part 15.247 has a special clause for beam forming devices. For non-beam forming devices the maximum output power is 30dBm, assuming an antenna of 6dBi. For each added 1dB of antenna gain, the output power must be decreased by 1dB. Since this each +1dB of antenna gain must be offset by losing 1 dB of output power, the maximum EIRP is 36dBmi. For beam forming devices the maximum power is 30dBm, assuming an antenna of 6dBi. For each added 3dB of antenna gain, the output power must only be decreased by 1dB, allowing a net EIRP increase of 2 dB (3 dB-1 dB) for each 3 dB of antenna gain added. Consequently, the maximum EIRP for beam forming devices may surpass 36 dBmi. Note: According to the FCC, in beam forming devices the antenna-array gain is defined as the gain of a single antenna element + 10log (# of elements).
