Nearfield parametric sources of rectangular aperture

Abstract

This paper describes a useful nearfield parametric source model for rectangular apertures of large aspect ratio. The model is based on a technique which has been successfully applied to circular apertures by J. C. Lockwood in a companion paper presented in this session. Specifically, the interaction region is subdivided into elemental virtual source apertures which radiate difference frequency energy. The existence of diffraction effects depends on the size and curvature of the virtual aperture and its distance from the field point. When diffraction is important, a field point may reside in the nearfield, cylindrical region, or farfield of an aperture. Lossless correction factors are derived which permit nearfield secondary source level and beampattern predictions to be made using a farfield parametric source model such as that developed by Moffett, Mellen, and Konrad (7th Int. Symp. Nonlin. Acoust. (August 1976), p. 19–21. This relatively simple model permits rapid computation of parametric source performance in the nearfield region. A comparison is given between predictions made using the model and those obtained from an exact numerical solution.