Corrections to "Time Domain UTD-PO Solution for the Multiple Diffraction of Spherical Waves for UWB Signals" [Apr 11 1420-1424]

In the above-named article (ibid., vol. 59, no. 4, pp. 1420-1424, 2011) the fourth sentence in "Section II Theoretical Models" should be revised as presented here. Reference [2] should be added because during P. Liu\´s preparation of [1], some words from [2] may have been used.