Hybrid wavefront-resonance representation for transient scattering by an open cavity

Short pulse scattering signals furnish valuable information for classification or identification of radar signature. For targets comprising of open-ended enclosures with interior-exterior coupling an effective parametrization of the scattered field is provided by expressing the contribution of the internal field and of the wave interactions around the exterior boundaries in terms of complex resonances and traveling waves, respectively. This furnishes a compact representation of the early time observables in the form of rapidly decaying external ray interactions and late time high-Q resonance observables which are structured around the more prominent internal partial resonances. This hybrid concept is illustrated here for the prototype configuration of a open ended perfectly conducting parallel plate waveguide, cavity. We introduce a systematic matrix procedure which may actually be applied to other open cavity configurations. The properties of the hybrid parametrization are contrasted with those of the global SEM representations. The numerical calculations construct the early time field as a rapidly decaying series of external wavefront interactions, while at intermediate times the internal resonances synthesize the dispersive guided mode return. Finally, the late time observables carry the signature of a cluster of high-Q internal resonances that occurs near modal cutoff frequency, in the form of slowly decaying typical waveform which is independent of the incident angle or of the excitation pulse but is related to the cavity dimensions.