On the Extended Thin-Wire Kernel

A number of recent works have shown that moment-method solutions of Hallén's and Pocklington's equations with the approximate kernel present undesirable and unphysical oscillations near the ends of the antenna and possibly (depending on the feed model) near the driving point. Such oscillations have been associated with the nonsolvability of the underlying integral equations. They necessarily occur when the number of basis functions is sufficiently large and cannot be blamed on finite computer word length or matrix ill-conditioning effects. In this communication, we show that similar phenomena occur when one uses the extended thin-wire kernel, originally proposed by Poggio and Adams in the 1970s and currently used by the Numerical Electromagnetics Code, which is an antenna modeling software suite that has many variants (e.g., GNEC, EZNEC Pro, SuperNeC, MiniNEC). We discuss the nature and properties of the oscillations. In particular, we show that they are milder and less rapid than those with the approximate kernel. Our main tools of study are: 1) numerical investigations that carefully distinguish from effects due to roundoff and 2) an analytical study for the case of the antenna of infinite length. We finally apply the so-called effective-current method as a remedy to the issues arising from the said oscillations.