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Angular aperture

About: Angular aperture is a research topic. Over the lifetime, 1771 publications have been published within this topic receiving 27257 citations.


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Journal ArticleDOI
TL;DR: In this paper, the point of maximum intensity in a focused aberration-free wave is not at the geometrical focus, but is closer to the focusing lens, where the waist of the beam is assumed to be located in the aperture plane.

161 citations

Journal ArticleDOI
TL;DR: In this paper, a critical examination is made of the somewhat loose and incomplete statement that a polar diagram is the Fourier transform of an aperture distribution, and it is shown that if the aperture distribution is of such a nature that the concept of polar diagrams is applicable at sufficiently great distances, then the polar diagrams are equal to the angular spectrum.
Abstract: A critical examination is made of the somewhat loose and incomplete statement that a polar diagram is the Fourier transform of an aperture distribution. By aperture distribution it is necessary to understand, in the two-dimensional case, distribution across the aperture of the component along the aperture plane of the electromagnetic field in the plane of propagation. Furthermore, the concept of the polar diagram has to be replaced by that of an angular spectrum, except in the common case when the aperture may be considered more or less limited in width, and the field is being evaluated at a point whose distance from the aperture is large compared with the width of the aperture (and the wavelength). For example, it is convenient for some purposes to regard the problem of diffraction of a plane wave by a semi-infinite plane screen, with a straight edge, as a problem about an aperture distribution in the plane of the screen. This is a case for which the concept of a polar diagram is not in general applicable, and has to be replaced by that of an angular spectrum. The field at all points in front of a plane aperture of any distribution may be regarded as arising from an aggregate of plane waves travelling in various directions. The amplitude and phase of the waves, as a function of their direction of travel, constitutes an angular spectrum, and this angular spectrum, appropriately expressed, is, without approximation, the Fourier transform of the aperture distribution. If the aperture distribution is of such a nature that the concept of the polar diagram is applicable at sufficiently great distances, then the polar diagram is equal to the angular spectrum. But the angular spectrum is a concept that is always applicable, whereas the polar diagram is one that is liable to be invalid (for example, in the Sommerfeld theory of propagation over a plane, imperfectly reflecting earth).

160 citations

Journal ArticleDOI
TL;DR: A more realistic camera model which approximates the effects of a lens and an aperture function of an actual camera is extended to allow the generation of synthetic images which have a depth of field and can be focused on an arbitrary plane.
Abstract: This paper extends the traditional pinhole camera projection geometry used in computer graphics to a more realistic camera model which approximates the effects of a lens and an aperture function of an actual camera. This model allows the generation of synthetic images which have a depth of field and can be focused on an arbitrary plane; it also permits selective modeling of certain optical characteristics of a lens. The model can be expanded to include motion blur and special-effect filters. These capabilities provide additional tools for highlighting important areas of a scene and for portraying certain physical characteristics of an object in an image.

152 citations

Journal ArticleDOI
TL;DR: Equations giving the intensity, the divergence, and the radius of the modified beam are derived in simple practical form for experimentalists and show that, even in the case of negligible power losses through the aperture, the diffracted beam characteristics may appreciably differ from those of the incident beam.
Abstract: A Gaussian beam weakly diffracted by a circular aperture can be approximated in the far field by another Gaussian beam with slightly different characteristics. Equations giving the intensity, the divergence, and the radius of the modified beam are derived in simple practical form for experimentalists. These approximated formulas show that, even in the case of negligible power losses through the aperture, the diffracted beam characteristics may appreciably differ from those of the incident beam. In a first approximation, diffraction effects may be ignored only if the ratio a/r(0) of the aperture radius a to the l/e intensity beam radius r(0) in the aperture plane is larger than 3.

146 citations

Proceedings ArticleDOI
02 Sep 2004
TL;DR: In this paper, point scattering center images for narrowband, wide angle data are investigated and the effect of limited persistence on the resulting images is investigated. But coherent processing of the entire wide angle aperture may not be the best image formation strategy for objects of practical interest.
Abstract: We consider imaging strategies for synthetic aperture radar data collections that span a wide angular aperture. Most traditional radar imaging techniques are predicated on the assumption of isotropic point scattering mechanisms, which does not hold for wide apertures. We investigate point scattering center images for narrowband, wide angle data, and consider the effect of limited persistence on the resulting images. We investigate imaging strategies that apply to wide angle apertures. We show that coherent processing of the entire wide angle aperture may not be the best image formation strategy for objects of practical interest. Finally, we present initial results on resolution enhancement techniques for wide angle apertures.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

143 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20234
20224
20217
20207
20195
201811