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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Recent advances in electromagnetic synthesis and analysis of dual-shaped reflector antennas

Dual-shaped reflectors have been used for many years. Thus, these reflectors have been used as high gain antennas on Voyagers 1 and 2. The objectives of the geometrical optics (GO) dual shaped synthesis are considered. Concerning the synthesis of dual shaped reflectors, it has been shown for circular symmetric reflectors that an exact GO solution can be found to the problem of transforming, by two reflections, any feed pattern into any aperture distribution. This problem involves solving two simultaneous nonlinear ordinary differential equations. The same approach for offset geometry leads to two simultaneous nonlinear partial differential equations. It is shown that these equations could also be integrated numerically, except that in general these equations are not total and therefore, in general, they do not have a 'smooth' solution. It is further shown that the offset partial differentials often very nearly form a total differential in many cases of practical importance.

Galindo-Israel, V.↗
NASA NTRS1993

Evaluation of frequency-selective reflector antenna systems

The performance of a four-frequency (S/X/Ku/Ku bands) frequency-selective surface (FSS) with double-ring elements (the type of geometry particularly well suited for the circular polarization requirement of the NASA's Cassini project) is evaluated for a planar and a curved FSS subreflector in a dual reflector antenna system. Good agreement is obtained between the calculated and measured data for the planar FSS model. The FSS effects in a four-frequency Cassegrain reflector antenna were accurately evaluated by taking into account the surface curvature and the FSS subreflector's transmitted/reflected field variation as functions of the polarization and the incident angles with respect to the local coordinates.

Wu, T. K.↗
NASA NTRS1979

Deployable antenna reflector

The first phase in the development of a solid surface, deployable, antenna reflector is outlined and discussed. The deployment concept is described in conjunction with illustrations and photos of the fabricated reflector models. Details and results of the thermal distortion analysis are presented. Results indicate that the discussed reflector concept is an effective approach in satisfying the requirements for large deployable antennas in the 6 GHz to 100 GHz frequency regime.

Palmer, W. B.↗
NASA NTRS1981

A new approach for synthesizing dual reflector antennas

It is pointed out that the offset geometry for dual reflector antennas is attractive for satellite communications where low side lobes are necessary to achieve good isolation between adjacent main lobes operating over the same frequency band. A description is presented of a new, numerically rigorous technique for synthesizing dual offset reflectors. The objective of the synthesis procedure is to transform a given primary feed pattern into a desired aperture distribution through two reflections in an offset dual reflector system. It is found that a given specification for the aperture distribution does not always lead to a smooth solution for the two surfaces. In this event, the so-called energy condition on the specified amplitude distribution is relaxed, and an approximate solution which satisfies the energy condition only within a certain numerical tolerance is derived.

Mittra, R.↗
NASA NTRS1985

On an algorithm for analysis of the radiation patterns of dual reflector and segmented reflector antennas

An algorithm has been developed to calculate the radiation patterns of a large reflector antenna for space applications. The algorithm treats each panel in the reflector array as an analytic surface having n-sided polygonal boundaries. The radiation fields for individual panels are computed and stored separately, and then added to yield a uniform radiation pattern for the entire reflector. Numerical methods developed to reduce the overlap of the aperture fields of adjacent panels are described in detail. Calculations of the tangential field components of the aperture plane are carried out based on the principles of geometric optics (GO). Some radiation patterns calculated with the algorithm are compared with patterns produced by other methods, together with measured data for a classical Cassegrain antenna and the calculated patterns are illustrated.

Christodoulou, C. G.↗
NASA NTRS1994

Making Precise Antenna Reflectors For Millimeter Wavelengths

In improved method of fabrication of precise, lightweight antenna reflectors for millimeter wavelengths, required precise contours of reflecting surfaces obtained by computer numberically controlled machining of surface layers bonded to lightweight, rigid structures. Achievable precision greater than that of older, more-expensive fabrication method involving multiple steps of low- and high-temperature molding, in which some accuracy lost at each step.

Sharp, G. Richard↗
NASA NTRS1990

Measured performance of the half-scale accurate antenna reflector

A corrugated horn was designed and fabricated for use as a feed for the half-scale accurate antenna reflector. This feed allows the reflector to be used in a compact range configuration as part of a microwave reflectance measuring system. The horn design is described, and the measured farfield patterns of the horn are presented. The horn was installed at the focus of the reflector, and the nearfield of the antenna was measured. The results of these measurements are presented and discussed with respect to the compact range application.

Lambert, Kevin M.↗
NASA NTRS1981

Techniques for prediction of large nonanalytic reflector antenna performance

Projected spacecraft missions for communications, radio astronomy and earth observations indicate a need for very large (on the order of 100 meters) space deployable or erectable antennas. This paper discusses a numerical method of analyzing reflector characteristics which is applicable to large reflector antennas whose surfaces are subject to mechanical and thermal distortions as well as fabrication and deployment errors. A technique of describing nonanalytic surface configurations by a finite number of known (measured) points was successfully applied in a computer model to predict the RF radiation pattern of a reflector using aperture plane integration techniques. The accuracy of the results is shown to be both a function of the number of measured points used and of their distribution.

Moskowitz, S. M.↗
NASA NTRS1985

Directivity optimization of a reflector antenna with cluster feeds - A closed-form solution

The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of single feed is used to control a beam. A closed-form solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 lambda parabolic reflector scanning 10 beamwidths, the optimum directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimum-directivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 lambda, it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d less than 0.5 lambda, the optimum design may exhibit the supergain phenomenon, namely extremely high directivities achieved by an oscillatory cluster excitation.

Lam, P. T.↗
NASA NTRS1963

The mechanical design of the horn-reflector antenna and radome

This paper describes the mechanical design of the horn-reflector antenna and the associated radome. The mechanical considerations dictating the final configuration of the antenna structure are discussed, along with the engineering aspects of the design, fabrication, and erection of the structure. The mechanical features of the data take-off and antenna drive systems are given in detail. The final section presents an account of the requirements, manufacture, and installation of the radome and its accessory equipment.

HORN ANTENNA↗
NASA NTRS1968

Computer program aids dual reflector antenna system design

Computer program aids in the design of maximum efficiency dual reflector antenna systems. It designs a shaped cassegrainian antenna which has nearly 100 percent efficiency, and accepts input parameters specifying an existing conventional antenna and produces as output the modifications necessary to conform to a shaped design.

Firnett, P.↗
NASA NTRS1980

Focal axis resolver for offset reflector antennas

Described are electrical means for determining the focal axis of an offset reflector antenna whose physical rim is not coincident with the boundary of the electrical aperture. Even and odd sensing functions are employed in the focal region, leading to both amplitude and phase criteria for resolving a focal axis generally inclined with respect to the system axis. The analytical aspects of the problem are discussed, and an example related to a 4-meter Large-Antenna Multiple-Frequency Microwave Radiometer (LAMMR) is included. The technique is useful for focal axis determination in mathematical simulations and in the physical world.

Schmidt, R. F.↗
NASA NTRS1961

Project Echo: Horn-Reflector Antenna for Space Communication

This paper describes the mechanical features of the horn- reflector antenna used for receiving signals reflected from the Project Echo balloon satellite, and presents in some detail the electrical characteristics (radiation patterns and gain) measured at a frequency of 2390 Mc. Theoretically derived characteristics which agree very well with the measurements are also presented; details of the calculations are given in the appendices.

Crawford, A. B.↗