Comments on “Systematic Design Technique for Dual-Band Branch-Line Coupler Using T- and Pi-Networks and Their Application in Novel Wideband-Ratio Crossover”

In the above paper, the authors propose a new design method for dual-band branch-line coupler. However, two errors have been found and some parameters are assigned partially. For clarification of the formulas of this design, the design equations are rededuced and the previous error equations are rectified. Then, the missing possibility is analyzed, which expands the band-ratio range. For proving the validity of this design, two simulations are implemented.