Showing papers on "Parabolic reflector published in 1971"

New technique for beam steering with fixed parabolic reflectors

Abstract: A technique is described which offers the potential of achieving wide-angle beam steering with fixed parabolic reflectors. The technique involves a primary-feed device with an aperture field distribution which can be adapted to match the distorted field distributions resulting from a parabolic reflector when an off-axis plane wave is incident. To provide an adaptation without deterioration of the system signal/noise ratio, which requires only a movement of the primary feed along a given locus and an adjustment of noninteracting phase shifters, the primary feed carries out a spatial Fourier transformation of the intercepted fields. The technique has been implemented in an experimental X band antenna and beam steering of ±15 beamwidths achieved with negligible distortion of the directional pattern and less than 0.5 dB loss in gain.

Theory of Certain Diffraction Gratings Produced by the Holographic Method

Abstract: It is now well known that a system of interference fringes photographed on a photographic plate has very interesting properties when used as a diffraction grating. This paper considers two cases. One is when the photographic plate is a plane surface; the aberration properties of this are worked out as a function of wavelength. There are three positions for which the spherical aberration is zero. Of these, one is of little interest as this is simply zero-order position. Another case considered was that of a photographic plate in the form of a concave spherical surface. In this case, there are three positions at which the spherical aberration is zero. The nature of variation of spherical aberration between these zero-aberration positions is presented in the form of curves computed from the theory of these gratings.

Composite antenna feed

Abstract: A composite antenna feed subsystem concentrated in a small area at the prime focus of the parabola of a satellite parabolic reflector accomodates a plurality of frequency bands. The arrays comprising the subsystem are mounted on the top cover of a communication module. A multimode horn is arranged at the center of the subsystem axis which functions at X- and C-band frequencies, and a cross-array consisting of individual elements form the S-band feed, with one arm of the S-band array containing an element mutually shared with the L-band array. Provision is also made for UHF frequencies, and a dipole arrangement for VHF frequencies is arranged around the S-band arms.

Photoelectric length measuring apparatus

Abstract: A beam from a light source traverses a first diaphragm having a slit therein and then a second diaphragm having different sized openings to form first and second partial beams. The two partial beams go through an inclined partially-transmission partially reflective mirror to a reflective rotor. The reflective rotor is positioned at the focal point of a parabolic reflector strip so that the light therefrom is projected at the focal plane of the strip. At the focal plane is a raster reflector and a cylinder lens. The cylinder lens projects the first partial beam across the area within which is the object to be measured. At the opposite side of that area is a reversing reflector. The reflected partial beams from the reversing reflector and the raster reflector go back via the parabolic reflector, the reflective rotor and the mirror to respective photoelectric receivers. The signal from the receiver getting the first partial beam opens an ''''and'''' gate for the period during which the first partial beam is blocked by the object. The light pulses from the second partial beam produce electrical pulses that go through the ''''and'''' gate for so long as it is open.

Radar monopulse antennas with converting polarization

Abstract: A monopulse antenna comprising an assymetrical parabolic reflector illuminated by a monopulse horn. A circular polarizing array cover adapted for selective emplacement over the horn aperture is provided. Changing from linear to circular polarization by placing the polarizer, by itself, over the horn produces an angular shift in antenna boresite (axis). A dielectric lens is provided for insertion over the polarizer to introduce a linear corrective phase shift, thereby eliminating the said axis shift.

Luminaire for area lighting

Abstract: This luminaire includes an elongated generally horizontal light source, a multiple section generally parabolic reflector disposed behind the light source, and a refractor in front of the light source. The reflector includes two symmetrical transversely disposed paraboloid sections with the light source at the focus of both sections to produce essentially two spaced brams of reflected light. The area between the beams is illuminated by direct light which passes through a control lens to form a third beam. The overall effect is essentially a rectangle of light of generally uniform intensity suitable for lighting a rectangular area such as a roadway from a luminaire set back from the roadway.

The calculation of electromagnetic fields in the Fresnel and Fraunhofer regions using numerical integration methods

Abstract: Some results obtained with a digital computer program written at Goddard Space Flight Center to obtain electromagnetic fields scattered by perfectly reflecting surfaces are presented. For purposes of illustration a paraboloidal reflector was illuminated at radio frequencies in the simulation for both receiving and transmitting modes of operation. Fields were computed in the Fresnel and Fraunhofer regions. A dual-reflector system (Cassegrain) was also simulated for the transmitting case, and fields were computed in the Fraunhofer region. Appended results include derivations which show that the vector Kirchhoff-Kottler formulation has an equivalent form requiring only incident magnetic fields as a driving function. Satisfaction of the radiation conditions at infinity by the equivalent form is demonstrated by a conversion from Cartesian to spherical vector operators. A subsequent development presents the formulation by which Fresnel or Fraunhofer patterns are obtainable for dual-reflector systems. A discussion of the time-average Poynting vector is also appended.

Radiation patterns of paraboloid with log-periodic dipole feed

Abstract: The effect of axial displacement of phase centre on the secondary performance of a parabolic reflector is described, with particular reference to a log-periodic dipole-array feed. Computed and experimental results are presented.

Light exposure apparatus and method

Abstract: A light exposure apparatus and method is provided herein wherein a workpiece to be exposed is transported through an area illuminated by collimated light. The collimated light is provided by a point source of high intensity light and a parabolic reflector.

Helical feeds at millimetre wavelengths

Abstract: The properties of helical aerials have been investigated between 26.5 GHz and 40 GHz. Beamwidths and polarisations are given as functions of helix parameters and frequency. With a suitable choice of dimensions, helixes can be used successfully as broadband feeds for parabolic reflectors and lenses at millimetre wavelengths.

Car headlight parabolic reflector mfr

Abstract: The reflector foundation is electro-chemically prelacquered before the mirrored layer is applied as a fluid mass by continual rotation of the foundation body. The electro-chemical process provides a very good adherent for the rotation process finished and acts as an anti-corrosion guard on the outer surface.