An efficient Fourier transform algorithm for multitone harmonic balance

A novel Fourier transform technique is proposed for use in multitone harmon ic-balance (HB) simulations, It is shown that computations of multitone dis torted spectra reduce to efficient one-dimensional fast Fourier transform o perations when certain relationships exist between the sampling rate and fr equency components of the signal. The algorithm requires minimal initializa tion time and is readily incorporated into existing HE tools. It is especia lly useful when the number of input tones is very large, such as spectral r egrowth and noise-power ratio simulations. The method is demonstrated on th e example of a 5-GHz MESFET amplifier driven by a quadrature phase shift-ke ying modulated carrier.