The Magnetostatic Frill Source

The magnetostatic frill source (MsFS) is introduced as a convenient way to obtain the electric field from a coaxial aperture in a ground plane. This approximation simplifies the analysis of arbitrarily shaped monopole antennas since both radial and axial components of the electric field may be expressed in closed form. Antenna characteristics computed using the MsFS are shown to agree very well with theoretical and measured results for cylindrical, conical and spheroidal monopoles. To demonstrate the utility of this model, it is shown that a single filamentary loop of magnetic current equal to the driving voltage and with radius equal to the geometric mean of inner and outer radii of the coaxial aperture is quite adequate for most purposes. Limitations of this approximation are discussed.