Comments on “Compact Dual-Band Branch-Line Balun Using Only Two Impedances With High Band-to-Band Isolation for Cellular/WLAN Applications”

In the above article, Puram et al. (2025) proposed a design of dual-band branch-line balun (BLB) using dual-band distributed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Pi $ </tex-math></inline-formula> structure. The design of BLB is a variant of the conventional 3-dB rat-race coupler (RRC). The authors replaced six quarter wavelength lines of RRC using dual-band <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Pi $ </tex-math></inline-formula> structures. This idea is not new; there are several dual-band RRC works, which can be used as dual-band BLB. From <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref>, Fig. 2(a)], it is evident that the authors were familiar with the RRC and BLB relationship. However, the authors did not cite works related to dual-band RRCs.