Comments on “Decoupling efficiency of a wideband Vivaldi focal plane array feeding a reflector antenna”

The authors of the above-named article have provided a theoretical and experimental study of a dense focal plane array designed for new generation radio telescopes. There are some oversights regarding non-citation of previous work that deserves comments. 1) The authors have adopted the term "decoupling efficiency" to describe the effectiveness of matching the focal plane array to the incident power. This replaces the term "coupling efficiency" used by them in some earlier conference papers. The inappropriateness of using the latter term was first indicated to the original authors by the present author in private correspondence. Related to this, it is noted that the term "coupling efficiency" has already been adopted by the fiber optics community where its meaning is directly opposite to the present one. Though the appropriateness of the term "decoupling efficiency" still requires further discussion, the new name should help to avoid confusion. 2) In Fig. 8, the authors have given the formula for the ideal efficiency of a small radiating element imbedded in an infinite dense array with a reference to their recent paper (DOI = 10.1016/j.aeue.2009.02.011) Such a reference may create the incorrect impression about the origin of the formula determining the ideal array element efficiency. This concept was originally considered by other authors in 1964 and 1967, where the expression for the ideal element efficiency is given. The authors?? formula differs from the formula in 1967 only by notation.