Comments on “A Rigorous Design Methodology for Compact Planar Branch-Line and Rat-Race Couplers With Asymmetrical $T$-Structures”

Abstract

In the above paper, the high–low impedance (HLI) section and its characteristic impedance of $Z_{\rm HLI}$ are suggested to reduce the size of branch-line and rat-race couplers. The characteristic impedance of $Z_{\rm HLI}$ , however, appears to be incorrect for the application of the asymmetric structures, such as the HLI sections.