A method for computing the input conductance of an electrically small antenna

An expression based upon the effective aperture area of an antenna is derived which relates the input conductance at the feed point to an integral involving the magnitude of the short circuit current at the same point when the antenna is used as a receiving element. Using this relationship the input conductance for an evanescent TM(01) circular waveguide mode inside and near the end of a finite-length thin (Omega = 2 ln (2h/a) = 10) cylinder is calculated over a wide range of electrical lengths including those for which the antenna is very short to those on the same order of a free-space wavelength, specifically kh = 0.05 to 3.5.