Low intermodulation RF amplifiers for MMDS applications

Summary form only given. An amplifier where the third order IM distortion has been reduced is proposed, If two signals at different carrier frequencies are incident at the input of an amplifier, due to the nonlinearity, these signals will interact with each other and the output will contain additional signals at all combinations of sum and difference of these frequencies, which are IM products. The injection of the second harmonics of the two inputs in the amplifier together with the fundamental signals will produce additional IM products at the output. By proper selection of phase and amplitude of the injected second harmonics, it is possible to make the third order IM products produced by the second harmonics and the original third order IM products out of phase and equal in amplitude. As a result third order IM products will be eliminated, in principle. The output spectrum of the RF power amplifier is given.