Showing papers on "Angular aperture published in 1984"

Focusing of electromagnetic waves through a dielectric interface

Abstract: Given a time-harmonic electric-current distribution over a finite planar aperture situated in front of a dielectric half-space, the transmitted field in the dielectric half-space is calculated by the plane-wave-spectrum technique. We concentrate on the current distribution that focuses the electromagnetic energy into a small spot in the dielectric medium, such as in hyperthermia applications. Numerical results are given to illustrate the variation of spot size and of focal-point electric-field intensity as functions of polarization, scanning, and the permittivity of the half-space. We find that (1) the maximum electric-field intensity is not at the focal point but rather at a point closer to the aperture; for a small aperture, this focal shift may be more than one wavelength; (2) when the dielectric half-space is introduced, the 3-dB spot size changes according to the ratio of the wavelength in the half-space to that in the original aperture medium; and (3) the electric-field intensity at the focal point is greatest when the permittivity of the half-space is less than that of the aperture medium, not when the two media are electrically matched.

Equivalence of surface current and aperture field integrations for reflector antennas

Abstract: The "extinction theorem" is used to prove that the fields of reflector antennas determined by integration of the current on the illuminated surface of the reflector are identical to the fields determined by aperture field integration with the Kottler-Franz formulas over any surface S_{a} that caps the reflector As a corollary to this equivalence theorem, the fields predicted by integration of the physical optics (PO) surface currents and the Kottler-Franz integration of the geometrical optics (GO) aperture fields on S_{a} agree to within the locally plane-wave approximation inherent in PO and GO Moreover, within the region of accuracy of the fields predicted by PO current or GO aperture field integration, the far fields predicted by the Kottler-Franz aperture integration are closely approximated by the far fields obtained from aperture integration of the tangential electric or magnetic field alone In particular, discrepancies in symmetry between the far fields of offset reflector antennas obtained from PO current and GO aperture field integrations disappear when the aperture of integration is chosen to cap (or nearly cap) the reflector

Automated-mode radius measurement using the variable aperture method in the far field

Abstract: The mode radius, a measure of the size of the LP01 mode, is considered an important parameter to specify and control in the manufacture of single-mode optical fibers. Of primary interest is the parameter's direct relationship to splice loss.

Focus condition detection device for cameras

Abstract: A focus condition detecting device of the type in which a pair of re-imaging lenses together with a condenser lens form a pair of re-images of an object image on a linesensor, such that the distance between the corresponding points of the re-images on the linesensor varies with the focus condition of a camera objective lens has an improved construction for positioning the linesensor with respect to the device with high accuracy. A field aperture mask having a field aperture is arranged optically behind a plane conjugate with the linesensor with respect to the re-imaging lenses and the condenser lens such that a pair of defocused images of the field aperture are formed on the linesensor by the re-imaging lenses and the condenser lens with respective one side blurred borders of the defocused images overlapping one another to make a V-shaped peak or dip of illuminance on a photocell of the linesensor located on the optical axis of the device, when the field aperture mask is uniformly illuminated. The device is formed into a module attachable on a camera.

Aperture illumination and antenna patterns

Abstract: The discussion of aperture systems will be continued in the present chapter with the object of developing in more detail the relations between the aperture field and the diffraction field. The results will furnish a basis for the design of the reflectors and lenses used in directive microwave antennas. The design considerations for such systems fall into two major groups: (1) transformation of the specifications that the radiation pattern of the antenna as a whole is required to meet into requirements on the aperture-field distribution, and (2) the design of the primary feed and reflector or lens to produce the required aperture field. The radiation pattern of the com posite antenna will be referred to as the secondary -pattern in distinction to the primary pattern of the feed system.

Photographic lens with large aperture ratio

Abstract: A photographic lens with a large aperture ratio comprises a plurality of lens elements brighter than F 1.5 and having a total covering power of at least 40°, with at least one of the lens elements being capable of passing an entire luminous flux focusing on a center of an image plane through at least 80 percent of a lens aperture thereof, and given a monotonous refractive index variation in the direction of an optical axis of the lens.

Manual aperture value setting circuit for camera

Abstract: A manual aperture value setting circuit for a camera in which digital values corresponding to the full-aperture value and the minimum aperture value of a lens mounted on a camera are applied from the lens in digital form to a logic circuit which operates so that, with the range of aperture value set on the side of the camera being maintained in the aperture value range of the lens, the aperture value which has been set is changed to the full-aperture value or the minimum aperture value of the lens when it is out of the aperture value range of the lens.

Satellite alignment sensor

Abstract: An optical alignment sensor capable of receiving radiation from a collima light source and subsequently providing orientation attitude and alignment data. Collimated light from the source impinges an aperture plate causing a shadow of the aperture plate pattern to fall across a two-dimensional photodetector array. Since the aperture pattern is larger than the active area of the array, only a portion of the light spots forming the aperture plate pattern will fall on the array. By varying the spacing of the apertures in the aperture plate in a known way, the light spots on the array can be associated with specific apertures in the aperture plate. From the location of specific light spots on the array, the angular orientation of the alignment sensor may be determined with respect to the incident beam.

Pattern distortion of aperture antennas radiating in the presence of conducting platforms

Abstract: An analytically simple and numerically efficient technique for calculating the pattern distortion of aperture antennas radiating in the presence of conducting platforms located in the near or far field of the antenna is presented. The technique presented, based on uniform geometrical theory of diffraction (UGTD), is also applicable for large aperture antennas (aperture area > 15 \lambda^{2} ). An excellent agreement between the calculated and measured results obtained for a typical aperture antenna mounted on a conducting platform confirms the validity of the analytical technique developed.

Large aperture ratio photographic lens system

Abstract: A large aperture ratio photographic lens system comprising a first lens group having positive refractive power, a second lens group having negative refractive power, a stop, and a third lens group comprising a negative lens element arranged in the rearmost position and having positive refractive power as a whole, the large aperture ratio photographic lens system being arranged to advance the lens system as a whole and, at the same time, to increase the airspace between the first and second lens groups when focusing on an object at a short distance from the state focused on an object at the infinite distance.

Scanning of sector and cosecant beams generated by a circular aperture

Abstract: A method of scanning a one-dimensional shaped pattern generated by a circular aperture is presented. It is shown that the desired beam shape can be retained in the desired scan plane by superposing on the nonlinear phase distribution applied along and parallel to the meridian plane, a linear phase progression along the perpendicular direction. Analysis carried out using the stationary phase method of evaluating the integral reveals that the gradient of the linear phase progression is a function of position along the meridian plane of the aperture. Expressions for the phase functions are derived. Computed results on the phase distribution and the radiation pattern are presented.

Variable aperture neutron collimator — II☆

Abstract: A second model of a completely adjustable, variable aperture neutron collimator has been developed. This redesigned model can be scaled to a full-size device appropriate for use in a medical facility. The collimator aperture can be easily adjusted to provide a square or rectangular cross-sectional exposure while maintaining a uniformly diverging line-of-sight from the neutron source.

Glass composition suitable for use in manufacture of lens having refractive index distribution and wide angular aperture

Abstract: PURPOSE:To obtain a glass composition suitable for use in the manufacture of a lens having a refractive index grade which decrases continuously from the central axis to the peripheral surface, by using a prescribed mol% each of SiO2, Tl2O, ZnO, ZrO2, Al2O3 and SnO or SnO2 as principal components and by providing specified relations among the components. CONSTITUTION:This glass composition contains, by mole, 35-80% SiO2, 4-26% Tl2O, 2-26% ZnO, 0-2% ZrO2, 0-8% Al2O3 and 0-5% SnO or SnO2 as principal components and satisfies four conditions represented by the equations. The glass has resistance to fused salt in an ion exchange stage, no vitrifying substance is formed on the surface of the glass, and the glass is not crystallized. The glass is suitable for use in the manufacture of a lens having a refractive index grade and >=40 deg. angular aperture. The lens does not cause deterioration in the degree of resolution due to coloring, devitrification or heterogeneity.

Line focus aperture for optical beams

Abstract: An aperture useful for spatially filtering a line focus of an optical beam, such as that produced by a cylindrical mirror or lens, comprises a pair of rotating smoothly polished cylinders.

Parabolic torus transreflector antenna

Abstract: The parabolic torus transreflector antenna is a circularly symmetric antenna which can be scanned through 360° by rotation of its feed alone. The reflector consists of a radome carrying 45° angled wires so that 45° polarised radiation is reflected on one side and transmitted by the other. A theoretical model has been developed to predict the radiation properties of this antenna for various feed configurations. An experimental torus has been constructed and tested, showing good agreement between theory and experiment. Good radiation patterns (sidelobes ≤ – 20 dB) are obtained with limited aperture efficiency (about 25% of the horizontal aperture). The theory shows how the phase aberrations and amplitude distortions in the radiating aperture, due to the antenna geometry, limit the sidelobe performance for wider aperture illuminations with a single horn feed. A linear array feed, designed to correct phase aberrations in one plane, is found to offer only a partial improvement if the full vertical aperture is required. It is concluded that greater aperture efficiency (≃45%), with sidelobes ≤ – 20 dB, requires either a torus with a restricted vertical aperture, (≤5 λ0), or a planar array feed.

Thirteen-part high-resolution lens for microreproduction engineering

Abstract: The invention relates to a thirteen-part, high-resolution, photographic lens having a large image field and variable aperture, for virtually diffraction-limited, distortion-free, five-fold reduction of an original, in particular in microreproduction engineering in the case of large-scale manufacture of integrated circuits in the field of micro-electronics. In this case, the optimum correction for a large field of 141 mm diameter is achieved by a constriction of the imaging bundle in the lens part situated on the object side in front of the aperture.

Characterization Of The Angular Aperture Of Step Index Fibres

Abstract: The experimental angular aperture of step-index fibres is always smaller than the theoretical aperture. Furthermore, the light power transmitted within the fibre up to the angular aperture is the more attenuated the greater the angle of incidence is. An expression of the light power transmitted within the fibre is given, which shows that the first phenanenon is due to variations of the fibre diameter core and the second phenamenon to the cladding absorbance.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Diffraction of He, Ne and H2 from Copper Surfaces

Abstract: We present an interpretation of diffraction data for He, Ne and H2 from copper surfaces in term of model potentials. These models are in a good agreement with theoretical calculations. These results prove that atomic (or molecular) beam diffraction can be readily used as a probe for quantitative surface structure determination.