Showing papers on "Cassegrain antenna published in 1975"

Some characteristics of a communication satellite multiple-beam antenna

Abstract: : The note describes a waveguide lens antenna system excited by a variable beam-forming network capable of producing a wide range of radiation patterns. These patterns vary from a narrow high-gain beam, equivalent to that of a steerable paraboloid, to the earth-coverage pattern of a wide-coverage communication satellite.

Gravitational deformation and astigmatism of tiltable radio telescopes

Abstract: An ideal telescope structure would deform, when tilted, in a homologous way, from one paraboloid of revolution to another one. Conventionally designed telescopes approach this condition already to some degree, special designs to a very high degree, and a measure for the degree of this approach is suggested. An equation is presented for the deviations from homology if an antenna is adjusted at zenith angle \theta and observes at angle \phi ; it contains only two structural parameters for alt-azimuth mounts (three for polar mounts). The choice of the best adjustment angle is discussed; this is basically different for both types of mount, and examples are given. Supported at two elevation bearings, conventional telescopes will generally show a strong gravitational astigmatism which may be corrected at the secondary mirror, thus improving the astronomical performance considerably. Two possible correction methods are suggested. Several of the equations presented are checked with the example of the 140-ft telescope at Green Bank, W. Va. Good agreement is obtained between detailed computer analysis and equations, and between analysis and astronomically obtained data. Suggested improvements for the 140-ft (applicable also to other telescopes) would diminish the deviations from homology by a factor of 2.5, and the remaining residuals then are brought below the internal inaccuracy of the surface panels. The astigmatic correction thus is advisable as well as sufficient.

Beam squint in circularly polarised offset-reflector antennas

Abstract: The beam-squint phenomenon, which is observed when offset portions of parabolic reflector surfaces are illuminated by circularly polarised primary feeds, can be a critical factor in the design of antennas employing frequency-reuse techniques. The letter describes the derivation of a very simple formula which can be employed to predict the magnitude of the beam-squint effect to an accuracy of better than 0.01 of the antenna halfpower beamwidth. Verification of the formula has been obtained using both computed and experimental data.

Frequency selective reflector system

Abstract: A dual- band Cassegrain antenna system operable at any polarization is described wherein the hyperbolic subreflector is made to reflect signals at a first band of frequencies and to transmit or pass signals at a second lower band of frequencies. The hyperbolic subreflector according to one embodiment is a square grid mesh with conductive rings centered along the connecting legs of the square grid mesh. The rings are approximately one-third wavelength in diameter at the first band of frequencies and act capacitively at the second lower band of frequencies. The inductive reactance provided by the conductive connecting legs of the grid mesh together with the capacitive reactance provided by the rings at the lower band of frequencies causes the subreflector to transmit signals at the second lower band of frequencies.

Shaped-beam horn-reflector antennas

Abstract: A design method for a horn-reflector antenna, which has a beam of arbitrary cross section, is developed. To show the effectiveness of the design theory, the measured data of an electrical model of Japan's domestic communications satellite antenna of this type are shown in comparison with calculated results. The design theory is based on geometrical optics, and is applicable not only to a horn-reflector antenna, but also to any reflector antenna. At the first step of the design theory, the shape of the wavefront near the aperture is determined to correspond to desired beam shape. The shape of the reflector is then determined by the law of the optical path.

A GTD analysis of the far-out sidelobes of cassegrain antennas

Abstract: Using recent developments of the geometrical theory of diffraction (GTD), the complete E - and H -plane patterns of Cassegrain antennas are computed. The pattern in the main beam region is computed by conventional aperture integration methods and the GTD analysis is used to evaluate the far-out lobes caused by spillover and by various edge diffraction processes. The effects of the edge curvature and surface curvature are included in the computations.

Corrugated horn fed offset paraboloidal reflector

Abstract: A high frequency antenna achieves low signal-levels in far-out sidelobe andacklobe antenna pattern regions through utilization of a corrugated feed-horn acting as a non-axial source for a cooperating parabolic reflector.

Multiple beam microwave apparatus

Abstract: A compact offset Cassegrainian antenna having a paraboloidal main reflector and a convex subreflector brings microwave beams to a focus. A small flat reflector placed in one of the beams at the focus deflects it for interception by a concave reflector and horn. Another beam passing by the flat reflector is intercepted by a second concave reflector and horn. The flat reflector is smaller than a focally located horn, allowing more closely-spaced beams to be accommodated. The flat reflector may be replaced by a curved reflector, a prism, or a microwave lens. Another flat reflector is added for each additional beam. Polarized beams are accommodated by adding a polarization screen.

Small broadband antenna having polarization sensitive reflector system

Abstract: A broadband antenna system of small dimensions and composed of at least one antenna having an associated design operating frequency, and a plurality of reflectors operatively associated with the antenna and disposed at respectively different distances therefrom, each reflector being spaced from the antenna and having a reflection characteristic to be optimally matched with the antenna for operation at a respective partial frequency band, each reflector being associated with a different partial band such that the total operating frequency range of the system is divided into a plurality of partial bands equal in number to the number of reflectors and covering the design operating frequency range and a further frequency range below the lower limit of the design range, whereby the antenna characteristics are improved, and in particular the operative bandwidth of the system is increased in the low frequency direction.

An extension of Rusch's asymptotic physical optics diffraction theory of a paraboloid antenna

Abstract: An extension of Rusch's asymptotic physical optics (APO) diffraction theory as applied to a parabolic antenna is presented. This extension provides a continuous solution throughout the shadow boundary region. The complete field expressions and the associated "new" physical optics diffraction coefficients are derived. Using the solution, the diffraction pattern for a 10-ft diameter focal plane parabola at 6 GHz is calculated.

Reflector surface error compensation in cassegrain antennas

Abstract: Two focal plane parabolic reflectors 2.8 m in diameter were used to test the feasibility of compensating for reflector surface profile errors by figuring the surface of a Cassegrain mirror. The paraboloids had been designed originally for frequencies less than 7 GHz, and therefore the surface errors had a significant effect on the antenna performance in the 27-40 GHz range. For these frequencies a template could be used to measure the surface profile. The first reflector had a prominent axially symmetrical surface error component. Compensating for this alone simplified the construction of the subreflector and improved the overall aperture efficiency at 34 GHz from 12 percent to 24 percent. The second reflector had a more random distribution of surface errors. Its efficiency was improved from 35 percent to 48 percent at 34 GHz, the improvement in gain varying from 1.1 dB at 28 GHz to 2.3 dB at 40 GHz, the shortfall being within 1 dB of the possible improvement predicted from the measured surface errors. For both reflectors the illumination efficiency set by the feed horn was about 50 percent. The linear cross polarization discrimination on axis increased from 29 dB to 38 dB at 34 GHz. The sidelobe levels and gain improvement obtained suggest that effective rms errors of about 0.45 mm with correlation distances of about 30 cm remained on the reflector surface after compensation, consistent with the estimated accuracy of the measuring and construction techniques adopted.

Some aspects of ground station antennas for satellite communication

Abstract: • A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.

Paraboloidal reflector offset fed with a corrugated conical horn

Abstract: A paraboloidal reflector, offset fed with a corrugated conical horn, has been examined as a possible antenna for use in millimeter wave communications systems when minimization of interference is an important consideration. Low far-out and back-lobe radiation were primary objectives. Experimentally obtained data, representative of performance at 37 GHz, is presented. When appropriately shielded to limit spillover, levels more than 75 dB below the main beam maximum have been obtained in the far-out and back-lobe regions.

The Design of Cassegrain Antennas for High Efficiency and Low V.S.W.R.

Abstract: This paper presents a method for optimally designing the subreflector of a Cassegrain antenna for maximum efficiency while maintaining a low VSWR level This is accomplished by setting up a composite performance criterion which explicitly includes both the efficiency and the power reflected back into the feed Gradient search procedures are then used to find the subreflector shape to maximise this criterion Broad band design is possible simply by integrating the criterion over the required frequency interval Theoretical and experimental results are given for a small two-reflector antenna

Off focus characteristics of the offset fed parabola

Abstract: The results of a theoretical and experimental investigation are presented for a dual mode horn fed offset parabola for feed displacements of \pm7 wavelengths about the focus in a direction along the offset axis. Beamwidths, sidelobe levels, relative gain, and crosspolarization patterns exhibit approximately equal E and H plane beamwidths as the feed is moved, along with wide angle sidelobes outside the main ridged beam that are similar in level to those of the same antenna with the feed on focus. The cross-polarization pattern levels diminish as the feed is moved off focus. The ridged main patterns have a shape similar to that of a corrugated horn with the same quadratic phase error. Therefore for some applications, it should be possible to use a defocused offset parabolic reflector rather than a corrugated horn, thereby effecting a sizeable decrease in antenna volume.

The effect of the polarization characteristics of the receiving feed on cross-polarization of receiving reflector antennas

Abstract: A method for calculating the co-polar and cross-polar radiation patterns of reflector antennas when operated in the receive mode is discussed. A formula for cross-polarization isolation is derived. Methods for cross-polarization reduction are discussed in the light of the obtained results. Numerical computations resulted in excellent agreement between the present method and previously used methods. Practical measurements also confirm the validity of the derived formulae and the conclusions drawn.

Antenna with a periscope arrangement

Abstract: In an antenna of the Cassegrainian or Gregorian type including a periscope arrangement, the auxiliary reflector has a longer focal distance than the auxiliary reflector of a conventional antenna of this type and the length of the optical path between the auxiliary reflector and the primary source of the antenna is choosen substantially equal to the distance between the auxiliary reflector and that one of its two foci which is the more remote therefrom. This makes it possible to use only plane mirrors in the periscope arrangement.

Offset cassegrain antenna

Abstract: PURPOSE:Reduction of the manufacturing cost of the main reflector through the segmentation of the mirror surface into common partial reflectors.

Study of efficiency of spherical Gregorian reflector

Abstract: The use of the current distribution method to analyse the field in the image space of a spherical Gregorian antenna when the main dish is illuminated by a linearly polarized plane wave is discussed. It is shown that the incident field distribution at the subdish is rather irregular, although it can be approximated by a smooth Gaussian distribution curve. In addition, it is possible to design a simple corrugated circular horn, so that the field at its aperture closely matches the incident field. As a result, a high efficiency wide-band system can be achieved.

Large Deployable Antenna Shuttle Experiment

Abstract: An experiment designed to use the Space Shuttle in tests of the mechanical and electrical properties of spaceborne deployable antennas under zero-gravity conditions is outlined. Space-erectable 20-meter diameter phased arrays or reflector/feed systems, and self-deploying mechanisms, are to be tested. Reflector surface integrity will be tested by an AM laser technique, and electrical behavior will be tested by a spin-stabilized RF beacon injected into orbit prior to unfurlment of the antenna. Focusing and gain measurements, static pattern measurements, dynamic RF gain measurements, and measurements of cross-polarized signals will be conducted, and the reflector will be illuminated by separate feeds for the S-, X-, and K-bands. Mechanical features of the mesh-wrapped rib furlable antenna design are described.

Earth Station Antenna using Reflecting Beam-Waveguide Feed

Abstract: The analysis and experimental evaluation of a reflecting beam-waveguide feed for an earth station antenna using two plane and two off-set paraboloidal reflectors is presented. Taking the mode matching theory in an optical resonator, the electromagnetic behavior of this feed is fully discussed. The measured RF performance of the earth station antenna using this feed is evaluated.

Antenna scanning apparatus

Abstract: A feed which is stationary relative to a parabolic reflector is located in close proximity to a prime focus of the reflector along its central axis. A moving element which is opaque to r.f. energy is moved along a path of revolution about the reflector axis, the path of revolution being located between the reflector and the stationary feed. The shape of the opaque element and the path of revolution are such that different portions of the aperture of the feed are masked as the element travels along the path of revolution. This imparts predictable scanning motion to the beam pattern which is coupled into the stationary feed. One highly useful embodiment of this invention is a construction in which the stationary feed is a secondary feed installed in a nutating feed antenna, and the nutating feed itself constitutes the opaque moving element.

A Multibeam Cassegrain Antenna

Abstract: This paper deals with generation of a multibeam pattern for three-dimensional radar surveillance by a stacked feed horn system installed in a Cassegrain antenna. Although its effective f/D-ratio is relatively high compared with the corresponding one of the primarily feed paraboloid, lateral displacement of feed horns in the focal plane results in strong pattern distortion caused by phase errors in the aperture plane. Investigations show that by means of an additional axial defocusing the quadratic term of these phase errors can be compensated improving the pattern distinctly, whereas the so-called Coma side lobe remains nearly unaffected. Basing on these results a feed horn system fulfilling special requirements was optimized and constructed. The obtained multibeam pattern of the Cassegrain antenna for the receiving case and the sectoral pattern for the transmitting case are shown.

Effect of conductive thermal-control paint on spacecraft-antenna performance

Abstract: The effect of applying a conductive thermal-control paint to the surface of a reflector antenna has been investigated at X band frequencies using a swept-frequency technique. With a particular space-qualified paint, a maximum boresight gain loss of 0.1 dB was recorded.

Crosspolarisation measurements using a composite feed

Abstract: The crosspolarisation performance of reflector antennas fed by a low-crosspolarisation composite feed is investigated experimentally. It is found that an improvement of slightly better than 9 dB can be obtained with this feed, compared with the single-dipole feed. This confirms previously published theoretical findings.