Some behavioral models for nonlinear systems include even-order nonlinear terms in their definitions that do not have a correspondence with the bandpass Volterra model. In this paper, an experimental characterization of the significance of even-order nonlinear terms is carried out based on a two-tone test for both a quadrature modulator and a power amplifier. Measurement results show that there are clear even-order terms at the output of the quadrature modulator but their levels are considerably weak. No significant even-order terms seem to be attributed to the power amplifier either.
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