Comments on "Efficient algorithms for spectra calculations in nonlinear microwave circuits simulators"

For the original article see IEEE Trans. Circuits Syst., vol. 37, no. 11, p. 1339-55, 1990. In the above paper by Ngoya et al., an improved discrete Fourier transform for almost-periodic signals (QOM-DFT) is presented. The advantages of QOM-DFT, especially its great improvement in saving CPU time are demonstrated in comparison with two other approaches: Least-Square Quasi-Orthogonal sampling method (LSQO) and Almost-Periodic Fourier Transform (APFT). However, it is necessary to point out that there are qualitative errors in the comparisons performed by Ngoya et al. because of their mistakes in using the data from a paper by X. Zhang et al.<>