Thin monopole antenna: finite-size belt-generator representation of coaxial-line excitation

The real system of a vertical monopole, obtained as a simple protrusion of the inner conductor of a coaxial line through the ground plane, is approximated by a monopole base driven by a finite-size belt generator. A simple formula is derived for determining the size of the belt generator so that it is equivalent to the coaxial-line excitation. The integral equation for current obtained with the finite-size belt generator is similar to the well known equation for the delta-function generator. However, the new equation has an integrable solution, convergent at all points. In particular, the monopole admittance obtained from the modified integral equation closely approaches, in the limit, the apparent admittance of the monopole, as measured by reflection measurements on the coaxial line and referred to the ground plane.