volume | PIER Journals

Abstract

Spectral decomposition in 2-D k_z-m space is used to develop transfer functions that relate modal electromagnetic fields on concentric cylindrical surfaces. It is shown that all time-average radiated power is generated by superluminal modes (phase velocity v_z > c) which are confined to the baseband |k_z| > k₀. Subluminal modes, with k_z outside of the radiated band, are radially evanescent but permit recovery of imaging resolution that exceeds the usual diffraction limit provided by the radiated fields. Outward translation between cylinder surfaces is found to have a stable low-pass 2-D transfer characteristic in k_z-m space, where spatial resolution decreases with increased radius. The inverse transfer functions for inward translation of field components (termed backpropagation) employ a high-pass process that amplifies subluminal evanescent modes, thus potentially enhancing resolution while also amplifying measurement noise. A 2-D filter with flat elliptical passband and Gaussian roll-off is used to mitigate noise amplification with backpropagation. Outward translation and backpropagation are tested using sampled data on finite-length cylinders for various noise levels.

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