Linearization of Radio-Relay Transmitters by a Predistortion Upconverter

A new principle for linearizing a radio-relay transmitter is described. The method operates according to predistortion principle and uses two parallel-connected upconverters whose operation points are set differently. One of the mixers has a high intercept-point, while the other works in the nonlinear region so that the output signal component is distorted. If the mixer configuration has nonlinear characteristics equivalent to those of the transmit amplifier, a cancellation of the distortion signals is possible. The principle has been tested in the 6-GHz band. A reduction of about 20 dB for 3rd-order IM products has been achieved. For an intermediate frequency of 70 MHz a bandwidth of about 30 ··· 40 MHz has been obtained.