Dipole antenna coaxially mounted on a conducting cylinder

The problem of a cylindrical dipole antenna symmetrically mounted on a conducting coaxial cylinder is analyzed both theoretically and experimentally. The theoretical approach is based on the Fourier transform solution for thin wire antennas, equivalence and image principles, point matching, and numerical optimization. The basic idea is that the modified dipole structure can be replaced by an equivalent system (as far as exterior fields are concerned) consisting of a simple perfectly conducting rod excited by an array of magnetic ring sources. The coefficients of these sources are then adjusted to match boundary conditions on the cylindrical modification surface. For the locations of the match points and sources, three gauges involving weighted integrals of the tangential electric fields are used to optimize the solution. Good agreements between measurement and theory have been obtained for the input admittances, resonance properties, and radiation patterns. Results are also presented for a dipole on a sphere to contrast effects due to change in modification shape.