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We consider certain characteristics of the radiation from collimated, ultrawideband short-pulse aperture distributions. It is shown that an efficient radiation must account for the multifrequency nature of the field. Two alternative schemes for wideband aperture synthesis of an impulse-like radiation pattern are examined. The first, entitled the 'Iso-width aperture,' utilizes only temporal shaping of the excitation pulse. In the other, the 'Iso-diffracting aperture,' we suggest source shaping in space-time so that all the frequency components in the field have the same collimation distance. The 'iso-diffracting' scheme yields higher directivity and more efficient pulsed radiation. Explicit examples for the pulsed source distribution and for the pulsed radiation patterns are presented, parameterized, and contrasted.

This paper is concerned with the behavior of transient wavefields due to a pulsed-beam (PB) wavepacket launched obliquely from a hypothetical aperture plane in a medium with generic dispersion k([Omega]), where k and [Omega] are wavenumber and frequency, respectively. This generalizes our previous investigation of a PB launched normally from the hypothetical aperture plane. The problem is solved through spectral decomposition into plane waves in the frequency ([Omega]) and spatial wavenumber ([Epsilon]) domains, followed by asymptotics on the spectral inversion integrals, with [Omega] synthesis performed before [Epsilon] synthesis. Special attention in the transient spectral domain is given to paraxial PB approximations and to criteria for their range of validity, which are expressed in terms of critical nondimensional estimators that contain the beam parameters as well as the dispersion parameters of the medium. The resulting PB's can be used to synthesize transient wavefields excited by arbitrary space--time source distributions of finite support on a specified aperture plane in the medium. Index Terms--Dispersive media, pulsed beam.

We investigate the plane wave spectral representations of the time-dependent relativistic electric and magnetic dyadic Green’s functions (GFs) of an isotropic dielectric-magnetic medium that is moving in a constant velocity. We distinguish two speed regimes in which the medium is moving slower or faster than its wave speed. Using a scalarization process for the EM vectorial problem, the EM dyads are evaluated from scalar GF. The spectral plane wave representations of the dyadic GFss are obtained using the those of the scalar ones according to the appropriate speed regime. We investigate the resulting spectral representations and the associated wave phenomena. Such spectral representations are essentials for solving different canonical scattering problems in which the sources are decomposed into time-dependent (transient) plane waves as part of the boundary problem solutions. [ABSTRACT FROM AUTHOR]