Modeling of Wideband Antennas by Frequency-Dependent Hertzian Dipoles

It has been found that a set of Hertzian dipoles can be optimized to model the radiation characteristics of an antenna. However, the existing models are normally for narrowband antennas and invalid for a wideband antenna. In addition, it is difficult to combine several such models at different frequencies into a wideband model because the interpolation of dipole parameters is not applicable. This paper presents a procedure to optimize a Hertzian dipole model for a wideband antenna, where each dipole parameter is a polynomial in the phase constant. The tangential electric field on a surface enclosing the antenna is first obtained by full wave analysis at multiple frequencies. An optimization method is then applied to determine the polynomial coefficients for each dipole parameter, by minimizing the error between the exact field and the field due to the dipoles. As an example, a wideband stacked dielectric resonator antenna (DRA) is modeled by four electric and three magnetic Hertzian dipoles. The dipole model is used to efficiently study the radiation characteristics of the DRA mounted on a circular ground plane. Moreover, it is pointed out that the dipole model is resistant to Gaussian noise added to the near-field data, and is frequency scalable.