Showing papers on "Feed horn published in 1975"

Some far-field studies of an offset launcher

Abstract: An offset paraboloidal reflector illuminated by a balanced feed horn constitutes an efficient launcher for coupling microwaves into quasioptical beams Measurements on a launcher with low blockage show low cross polarization The amplitude, phase, and polarization characteristics are predicted by two gaussian beam modes, and the resulting formulas are found to agree well with measurements at 19 and 28 GHz For example, with increasing offset angles, the ratio of the maximum cross-polarized signal in the radiation pattern to the on-axis co-polarized signal is observed to vary from −44 to −37 dB, within 1 dB of the predicted variation

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.

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.

A rectangular corrugated feed horn

Abstract: This paper presents typical results of measurements made on a square corrugated horn and also one with a small rectangular aperture that was designed to generate an elliptical beam for either of two orthogonally polarized signals.

Beacon tracking receiver

Abstract: A radio frequency receiver is responsive to signals radiated by a remote transmitter. The receiver includes at least one pair of antennas separated by approximately one-half wavelength at the transmitter frequency. The phases of the signals detected by the antennas are compared for the purpose of determining the relative direction to the transmitter.

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.

Waveguide-tuned phased array antenna

Abstract: A phased array radar antenna comprises an array of hollow, rectangular tubes, each tube having an opening therethrough. A tuning slug is positioned within each of the hollow tubes, and is mechanically coupled with a transducer for moving each tuning slug through the corresponding hollow tube responsive to an electrical input thereto. A feed horn is provided for radiating electromagnetic energy into the openings of the hollow tubes whereby the energy is reflected therefrom in a direction and in a beam width determined by the position of all of the slugs.

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.

Wide-band communication satellite antenna using a multifrequency primary horn

Abstract: The design method of and experimental results obtained from a wide-band satellite antenna with a multifrequency primary horn is described. This antenna can be used in 4, 6, 20, and 30 GHz frequency bands. Some measured data of the primary horn and the antenna are reported. Consequently, the antenna efficiency is about 45-50 percent in all the above frequency bands.

Ghost echoes on the Earth–Moon path

Abstract: ON July 7, 1974 while using a Moon Bounce technique on 1,296 MHz I observed the appearance of strange, delayed echoes. My equipment consists of a parabolic antenna 26 feet in diameter with a circularly polarised feed horn driven with 500-W continuous wave from a transmitter. The receiver has a noise figure of 2 dB and a bandpass of 500 cycles and the equipment had a very distinct note because of a spurious frequency near the fundamental; on the Moon–Earth circuit it is very easy to identify this signal because of this unique characteristic. On the day in question a series of dots or a single dash were being reflected back from the Moon after 2.6 s. Suddenly there appeared a second signal delayed by approximately 2 s. This signal had the same characteristics of the Moon Bounce signal except that it was weaker.

Nomographs for phase centers of conical corrugated and TE 11 mode horns

Abstract: Practical and convenient monographs, for obtaining the phase centers of corrugated conical horns and conical horns excited in TE 11 mode, are presented. Given the length of horn, the radius of aperture, and the distance from aperture to observation point along the horn axis, the location of the phase center can be directly found on these nomographs.

Antenna with echo cancelling elements

Abstract: A Cassegrainian antenna having a feed horn, a subreflector and a main reflector exhibits subreflector reflections back toward the feed horn. Some of this energy is reflected by the feed horn, and some by the main reflector adjacent to the feed horn, back toward the subreflector. This doubly reflected energy constitutes an echo which is reduced in the prior art by using a flat reflector plate mounted near the subreflector to cancel energy radiated by the subreflector back toward the region of the feed horn. Herein is disclosed the addition of a frequency sensitive reflecting wire grid between the flat plate and the feed horn. A combined reflection from the grid, plate, and subreflector provides echo cancellation in two frequency ranges. The plate may be recessed in a hole in the subreflector. A guard ring surrounding the plate prevents leakage through the subreflector hole.

Improvements in the Development of Coaxial Feeds for Paraboloidal Reflector Antennas

Abstract: The coaxial feed for front-fed paraboloidal antennas as known from previous papers, by which an increase of aperture efficiency and a decrease of spillover is achieved, was simplified considerably in construction and improved in bandwidth. The aperture field distribution of the feed, which is necessary for an approximately sector-shaped rotationally symmetric feed pattern, is achieved by the excitation and superposition of H12-, E11- and H11-modes, however, the modes are different from those superimposed in earlier constructions. The modes are excited by aperture coupling and the means of excitation are explained. The feed dimensioning was optimized experimentally. The aperture efficiency of paraboloids with these feeds will be reported.

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.

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.

The Calibration of a Large Paraboloidal Antenna using a Cryogenic Black-Body Enclosure

Abstract: The aperture efficiency of the 100-meter radiotelescope has been measured in the prime focus configuration at 5 GHz. Calibration was performed by inserting the feed-horn alternately in two specially designed black-body enclosures, the effective temperatures of which were provided by liquid nitrogen and liquid argon - a difference of 9.94 K. Radio sources of known flux density and brightness temperature were compared with the 9.94 K calibration, resulting in a 1.5 per cent uncertainty in the aperture efficiency. The sources of error are tabulated, and compared with those obtained by replacing the feed horn by waveguide loads.

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.

Design of multiple edge blinders for pyramidal horn reflector antennas

Abstract: The design of multiple edge blinders for pyramidal horn reflector antennas is discussed. The blinders eliminate high sidelobes in the azimuthal plane near 90\deg for horizontal polarization at 4, 6, and 11 GHz. The successful design of multiple edge blinders for simultaneous operation in each of the three common carrier bands depends upon the suppression of an off-axis major lobe at 4 GHz and grating lobes which typically appear at 6 and 11 GHz. Using the blinder array factor and element pattern, it is shown that these lobes can be suppressed by properly choosing the blinder tilt angle \beta_{c} , the inclination of an individual blinder edge \delta , and an adequate number of edges N .

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.

Summary of Radiation Pattern Measurements Using the LES-7 Lens and Variable Power Dividing (VPD) Feed Network at 7.68 GHz

Abstract: : A comparison between experimental and calculated radiation pattern data for a multiple-beam antenna is presented. The antenna consists of a waveguide lens aperture excited by a 19-element feed horn array and variable beam-forming network. The pattern data presented varies from a narrow high-gain beam, equivalent to that of a steerable paraboloid, to the earth-coverage pattern of a wide coverage communication satellite. Also discussed are the results of the earth-coverage measurements when either one or two feeds are turned off so as to produce nulls in the earth-coverage pattern.