Representation of the continuous spectrum excited by a dipole in a multilayer configuration through weighted cylindrical leaky waves

In this work, an original closed-form approximate evaluation is performed for the continuous-spectrum field excited by a dipole source in substrate-superstrate configurations, often employed in planar antennas and integrated passive components. By extending a recently-developed asymptotic approach, previously applied to the one-dimensional TE case of a line-source excitation, we first derive a suitable closed-form expression for the residual-wave field: this allows us to represent the continuous-spectrum field also in the neighbourhood of the transition region between leaky-wave and bound-wave ranges in the form of angular-dependent cylindrical leaky waves of TE or TM type, weighted by an appropriate transition function. The proposed formulation makes clear in a simple way the characteristics of the continuous-spectrum field excited by practical sources. Numerical results which show the accuracy of this approach are provided for different configurations and frequency ranges.