Comments on “Dual-Band Branch-Line Couplers With Short/Open-Ended Stubs”

Abstract

In the above paper (Feng et al., 2020) design of dual band branch-line couplers with short/open-ended stubs was presented. However, there are some major discrepancies & mistakes observed in the design equations and plots as well. For the case of dual band design using open-circuited stubs, it is found that the basic operation of the coupler is lost, where the through port behaves as isolated port and vice versa when attempted to design using circuit simulators with the impedances provided in (Feng et al., 2020). Here, corrected versions for the band ratio versus impedance plots for both dual-band couplers with short-ended and open-ended stubs are provided. Further, the correct design equations are derived and accordingly the correct simulation S-parameter plots for the dual-band couplers with open-ended stubs, along with corrected k values are given. Moreover, other minor typo errors to be noted for better readability for the research community are provided.