Abstract
The phase-difference performance at two desired frequencies of the generalized dual-band unequal coupler is discussed and presented in this comment as supplementary information. The condition of ${\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_1}}} + {\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_2}}} = \pi $ and the analytical equations for ${\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_1} \,\text{or}\, f_{2}}}$ are provided. It can be concluded that the dual-frequency output phase differences are constant and equal to 90° when ${R_2} = {R_3},$ but the values of ${R_1}$ and ${R_4}$ can be varied. Finally, the calculated results show that the phase-difference variations about $ \pm 11\% $ in the whole useful bandwidths of these branch-line couplers are objective and acceptable in common practical applications when ${R_2}$ and ${R_3}$ are in the range of 30–100 Ω $({R_2} \ne {R_3})$ .
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