Polyspectral models are a class of nonlinear behavioral models that were applied to power amplifiers over 20 years ago but have not seen subsequent development. Polyspectral models have a multiple-branch topology that is a special case of the Volterra series. They provide closed-form, optimum solutions to their constituting filters. Here we bring the model construction measurements up to date using modern test equipment. The two-branch version presented here is simple to implement and provides good accuracy and computational efficiency for system simulations. We present results for a GaN amplifier subject to orthogonal frequency-division multiplexing for signals of bandwidth up to 200 MHz.