<title>Analytic Continuation Applied To Microwave Apertures</title>

Abstract

Microwave holography is a useful experimental technique for imaging remote or inaccessible objects and for diagnostics of antennas, radomes, and scatterers; however, diffraction restricts image resolution. This paper describes a method for improving resolution in microwave holography. The holograms are either spherical or circular. Porter's scalar theory of curved holograms is extended to vector fields by using rectangular components to treat the effects of wave polarization. The mathematical formulation is a Helmholtz diffraction integral. This integral is written as a convolution for currents on line segments. The convolution is applied to the spatial frequency spectra of images. The spectra of dipole antennas are analytically continued, and the current distributions are exactly reconstructed. An experimental example is described; it is diffraction of a half-wavelength wide slit in a conducting screen. The analytic continuation of the holographically reconstructed nearfield produced images with resolution approximately 1/4 wavelength. Before continuation, resolution was 0.6 wavelength. In addition, the boundary condition of vanishing tangential over the metal screen was better satisfied in the image produced by continuation.