US Patent 7965990 Wireless backhaul power amplification using fourier transform matricies

An apparatus amplifies RF signals in a communication system by using a first directional coupler having at least two inputs and at least two outputs; at least two RF amplifiers, where an input of each RF amplifier is connected to a different one of the at least two outputs of the first directional coupler; and a second directional coupler having at least two inputs and at least two outputs, where each one of the at least two inputs is connected to an output of a different one of the at least two RF amplifiers. The at least two outputs of the second directional coupler are connected to at least two antennas, respectively.