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Showing papers on "Angular aperture published in 1967"


Journal ArticleDOI
TL;DR: The previous formula of Nagelberg for determining the location of the phase center of the aperture antennas was examined by calculating the phase patterns of a radiation field as mentioned in this paper, and it was shown that the phase centre should not be located at the aperture, but at the point determined by the expression derived here.
Abstract: The previous formula of Nagelberg for determining the location of the phase center of aperture antennas is examined by calculating the phase patterns of a radiation field. The results show that the phase center should not be located at the aperture, but at the point determined by the expression derived here.

13 citations


Journal ArticleDOI
TL;DR: In this paper, the focusing property of an aperture is investigated in order to determine how the focusing properties of the aperture depend on the length of coherence of the illuminating field. But the focus property becomes poorer as the coherence length decreases and the focus displaces itself toward the aperture.
Abstract: Fresnel diffraction from an aperture is investigated in order to determine how the focusing property of the aperture depends on the length of coherence of the illuminating field. The computations show how the focusing property becomes poorer as the coherence length decreases and the focus displaces itself toward the aperture.

10 citations


Journal ArticleDOI
01 Jan 1967
TL;DR: The statistical properties of the electromagnetic field diffracted by a plane aperture illuminated by a fluctuating field have been studied in the Fresnel zone on the basis of the theory of partial coherence as mentioned in this paper.
Abstract: The statistical properties of the electromagnetic field diffracted by a plane aperture illuminated by a fluctuating field have been studied in the Fresnel zone on the basis of the theory of partial coherence. The average power distribution and the amplitude and phase of the degree of coherence have been computed for several coherence lengths of the illuminating field ranging from 1/4 to 5 times the dimension of the aperture and for two geometries of the observation points. The obtained results indicate the limits of validity of the often assumed hypothesis of spatial stationarity and of the real Gaussian approximation for the degree of coherence of the diffracted field. It turns out also that the optimum position of a receiving phase-sensitive system placed in the field diffracted by an aperture may not be the focus of the aperture, since there the concentration of average power density is accompanied by a poor coherence of the field.

6 citations



Patent
26 Jun 1967
TL;DR: In this paper, a magnetic lens assembly for a corpuscular ray device has been proposed, which includes a pair of shielding cylinders which are coaxial and spaced from each other, which are made of a superconductive material, and which have their common axis coinciding with a lens axis of the lens assembly.
Abstract: A corpuscular ray device having a magnetic lens assembly. Although the invention is particularly applicable to objective lens assemblies of electron microscopes which operate under vacuum, it is also applicable to lens assemblies for ion microscopes, electron-diffraction devices, or other corpuscular ray apparatus wherein the rays are situated in tubular enclosures. The magnetic lens assembly includes a pair of shielding cylinders which are coaxial and spaced from each other, which are made of a superconductive material, and which have their common axis coinciding with a lens axis of the lens assembly, these shielding cylinders being surrounded by a lens winding which may also be made of a superconductive material and which serves to generate the magnetic field which is concentrated by the shielding cylinders in the region of the corpuscular ray. These shielding cylinders have directed toward each other a pair of end faces which are spaced from each other and define between themselves a lens gap which is devoid of any shielding components made of superconductive material. The aperture error constant of the lens assembly depends upon the maximum value of the field intensity in the lens gap and upon the field gradient along the lens axis in the lens gap. The magnitude of the lens gap is chosen in such a way that with a predetermined value of field intensity outwardly beyond the lens gap and the shielding cylinders the maximum value of the field intensity in the lens gap and the field gradient in the lens gap along the lens axis provide for the lens assembly an aperture error constant which is less than a predetermined value of aperture error constant.

1 citations