Showing papers on "Cassegrain antenna published in 1967"

A note on reflector arrays

Abstract: A Van Atta antenna array, which has a major lobe of the reradiated field in a direction retrograde to that of the incident wave for arbitrary directions of incidence, is analyzed in terms of the scattering matrix of the network interconnecting the antennas.

Application of spherical wave theory to cassegrainian-fed paraboloids

Abstract: In this paper the spherical wave expansion technique is used to analyze the general properties of paraboloidal antenna feed systems. As a result, fundamental aperture efficiency and noise temperature limitations are established as quantitative functions of antenna wavelength size. A boundary-value solution is found for synthesis of ideal subreflector shapes in a Cassegrain-type feed system. The resulting surface is found to reduce the classical hyperboloid in the limit of zero wavelength. Applications of this synthesis technique to high performance feed systems and subreflector matching are discussed. Finally, an interesting quantitative cross-check between vector spherical wave and vector diffraction theories is obtained.

Aperture feed for a spherical reflector

Abstract: The problem of designing a feed system for illuminating a spherical reflector is examined. A method is proposed for specifying the required field distribution over the aperture of the feed system, and the primary illumination and gain resulting from this distribution are derived. The results indicate that a significantly smaller feed aperture can be employed than would be indicated by conventional ray tracing methods. Specific numerical results are obtained by taking the Arecibo antenna as an example, for which a calculated aperture efficiency of 67.5 percent is possible with approximately a 38-foot-diameter aperture feed.

Digital computer analysis and design of a subreflector of complex shape

Abstract: Digital computer technique for computing scattered pattern of complex hyperboloid subreflector in Cassegrain antenna feed systems

The correcting feed at 611 MHz for the AIO reflector

Abstract: A correcting feed, illuminating a 600-ft circle of the Arecibo Ionospheric Observatory reflector, has been built at 611 MHz. The feed has two major components, a four-element linear array with a reflecting screen and a 16-element linear array. The antenna gain is 56 dB and the 3-dB width of the principal lobe is about 9 minutes of arc.

Shortened horn-reflector antenna

Abstract: A shortened horn-reflector antenna overcomes the mechanical disadvantages and complexity of the conventional horn-reflector antenna. The shortened antenna offers broadband performance, economic construction, very low antenna temperature, and excellent pattern performance.

An improved point-source compact antenna range

Abstract: : A point-source compact antenna range was modified by installing a range reflector having a more accurate surface contour and by shielding the reflector edge and its feed with absorbing material. Stray radiation measurements and pattern measurements were made within the band from 8.2 to 12.0 GHz using a 30-inch paraboloidal test antenna. Results are compared with those obtained on a previously constructed range, and they demonstrate that the range performance was improved. Measured maximum stray radiation levels on the modified range vary from about -44 db to about -58 db with respect to the collimated radiation. Radiation patterns compare very favorably with those measured on a 700-foot outdoor antenna range.

Improved point-source and line-source compact antenna ranges

Abstract: : A point-source and a line-source compact antenna range were modified by installing on each a range reflector having a more accurate surface contour and by shielding the point-source reflector edge and its feed with absorbing material. Stray radiation measurements and antenna pattern measurements were made on both ranges at X-band (8.2 to 12.0 GHz) frequencies using a 30-inch paraboloidal test antenna; these measurements also were made on the point-source range at C-band (5.4 to 5.8 GHz) and at S-band (2.8 to 3.2 GHz) frequencies using pyramidal horn antennas. Results at X-band frequencies are compared with those obtained on previously constructed similar compact ranges, and they demonstrate that the range performance was improved. Antenna radiation patterns compare very favorably with those measured on outdoor antenna ranges.

The Raisting Satellite Earth Station and Its System Noise Temperature

Abstract: Features of the German satellite earth station at Raisting are cited in this paper. One essential criterion, the noise performance, is discussed in particular. The 25-meter Cassegrain antenna with horn reflector feed (covered by a radome) has been subjected to extended measurements of the system noise temperature. The results show the relation between the system noise temperature and the antenna elevation and azimuth angles under different weather conditions. In fair weather the system noise temperature is 53/deg K with an elevation of 5° giving a ratio of antenna gain and system noise temperature of 40.7 dB. The curve of the system noise temperature at low elevation angles corresponds well to the optical horizon. During rain an increase of the system noise temperature has been noted. After rain, however, normal conditions are soon restored.

Reflector antenna zoom techniques.

Abstract: : This report describes a study and investigation of a reflector antenna system that provides zoom (variable beamwidth) and scan capability using controlled-aperture amplitude and phase. The antenna system is called a hybrid system since it uses a secondary phasor as both a lens and a reflectarray. The secondary phasor operates as a lens in conjunction with one feed for scanning in the receive mode and as a reflector in conjunction with another feed for zooming in the transmit mode. Switching between a zooming transmit mode and a scanning receive mode results in a versatile radar antenna with an inherent duplexing capability. Analysis of this system by digital computer to determine the optimum geometrical configuration is discussed. Component design of the elements, phase shifters, drivers, and beamsteering unit for the secondary phasor are also discussed particularly for operation at S-band. Considerations for scaling the system to UHF are presented. (Author)

The reflection coefficient of a parabolic-reflector antenna illuminated by a radiator with sector-shaped radiation pattern

Abstract: The use of a horn radiator with sector-shaped radiation pattern rednces the reaction of a rotation-symmetrical parabolic reflector to less than one quarter of the reaction with conventional horn radiators. No vertex plate is necessary.