Admittance correction factor for coaxially excited cylindrical antennas

A long standing problem in antenna theory has been the accurate determinati on of the input admittance of coaxially excited antennas. While reasonably accurate results have bee;l obtained for a range of problems using the so c alled "TEM approximation'' for the coaxial aperture electric field, these r esults nonetheless contain an error of small but unknown extent, By examini ng the infinite coaxially excited antenna problem this approximation error has been quantified and a simple approximation factor has been deduced, Thi s correction factor is applicable to a range of antenna problems having a c oaxial source geometry.