Comments on “A Simple and Universal Phase Control Method for Designing Directional Couplers With Adjustable Phase Difference Slope and High Linearity”

In the above article (Pan et al., 2023), it is shown that the solution given for the–90° directional coupler with adjustable phase difference slope is inadequate for equal power division purposes. The proposed solution results in a significant error between the two outputs of the coupler. Exact, correct solutions are derived for the coupler, which proves that the proposed solution in Pan et al. (2023) corresponds to the coupler for an unequal power division case rather than the equal power division.