Asymptotic Fields in Frequency and Time Domains Generated by a Point Source at the Horizontal Interface Between Vertically Uniaxial Media

For a point current source placed at the interface between two half-space media, investigation is made of the far-zone asymptotic fields in the frequency domain and their transient waveforms. The media are electrically uniaxial with the uniaxis normal to the interface. The leading-order fields contributed by the stationary-phase points serve as good approximations well off the critical angles. Near the critical angles, the uniform asymptotic techniques need to be employed for a proper approximation. Unlike the ordinary wave, the extraordinary wave cannot be correctly described merely by taking into account the proximity of the stationary and branch points, except in some rare cases. Consideration must also be given to the combined effect associated with the pole introduced in the formulation. The validities of the asymptotic approximations are examined in the time domain by comparing the asymptotic-field waveforms with the wavenumber-synthetic waveforms, around the critical angle of the extraordinary wave.