Input admittance of a thin dielectric-sleeved finite antenna excited by a uniform field

The input admittance of a long hollow conducting cylindrical antenna with an infinitely long dielectric sleeve surrounding it, and excited by a uniform field applied across a gap of a given width at the center, is determined by a variational method. A suitable trial field is chosen and the resulting integrals are evaluated asymptotically with the assumptions that the electrical radius of the antenna is small and its length is large. The final expression is easy to evaluate and some numerical results are presented.