Analysis of the second harmonic effect on power amplifier intermodulation products

A theoretical analysis is reported in this paper to investigate the effect that a second harmonic signal which might be present at an amplifier´s input has on generating additional intermodulation products, particularly the third-order inter-modulation (IM3) products. The analysis shows that the amplitude of an extra generated IM3 component is equal to the product of the fundamental amplitude, the second harmonic amplitude, and the second order Taylor series coefficient. The effect of the second order harmonic on the IM3 is examined through a simulated example of a 2.22-GHz 10-W Class-EF amplifier whereby the IM3 levels have been reduced by 2-3 dB after employing a second harmonic termination stub at the input.