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Results for “Antenna radiation patterns”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

A pattern synthesis technique for array feeds to improve radiation performance of large distorted reflector antennas

Technologies exist for construction of antennas with adaptive surfaces that can compensate for many of the larger distortions caused by thermal and gravitational forces. However, as the frequency and size of the reflectors increase, the subtle surface errors become significant and degrade the overall electromagnetic performance. Electronic compensation through an adaptive feed array offers a means for mitigation of surface distortion effects. A pattern synthesis approach for electromagnetic compensation of surface error is presented. The pattern synthesis approach uses a localized algorithm in which pattern corrections are directed toward specific portions of the pattern requiring improvement. The pattern synthesis technique uses radiation pattern data to perform the compensation.

Smith, William T.↗
NASA NTRS1986

Theoretical models of single-element LTSA antenna elements

The spectral domain computations for slotline guide wavelength and characteristic impedance provide the basic parameters that are need to calculate the radiation pattern of an Linearly Tapered Slot Antenna (LTSA) by using the half-plane Green's function and a stepped approximation to the LTSA structure. However, the spectral domain computations are somewhat time consuming and not suitable for computer aided design application. Therefore, the results of several computation were fitted by formulas that are readily evaluated on a calculator or computer. Antenna measurements were continued, and an attempt was made to predict the truncation effect by three different methods.

Source record↗
NASA NTRS1974

Aperture excited dielectric antennas

The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

Crosswell, W. F.↗
NASA NTRS1990

Coplanar-waveguide/microstrip probe coupler and applications to antennas

A method to couple microwave power from a coplanar waveguide to a microstrip line on opposite sides of a ground plane is demonstrated. The coupler uses a metallic post which passes through an aperture on the ground plane connecting the strip conductor of the coplanar waveguide to the microstrip line. The measured insertion loss and return loss are about 1 dB and 10 dB, respectively, across the frequency range of 0.045-6.5 GHz. To demonstrate potential applications of the coupler as a feeding network for a microstrip patch array, measured radiation patterns of two rectangular patch antennas with a direct coplanar-waveguide/microstrip feed and with a proximity coupled coplanar-waveguide/microstrip feed are presented.

Simons, R. N.↗
NASA NTRS1981

Airborne antenna pattern calculations

Progress on the development of modeling software, testing software against caclulated data from program VPAP and measured patterns, and calculating roll plane patterns for general aviation aircraft is reported. Major objectives are the continued development of computer software for aircraft modeling and use of this software and program OSUVOL to calculate principal plane and volumetric radiation patterns. The determination of proper placement of antennas on aircraft to meet the requirements of the Microwave Landing System is discussed. An overview of the performed work, and an example of a roll plane model for the Piper PA-31T Cheyenne aircraft and the resulting calculated roll plane radiation pattern are included.

Knerr, T. J.↗
NASA NTRS1983

Focusing the parabolic antenna

The focused parabolic antenna has far field pattern characteristics in the radiating near field region. Therefore, it can provide fine resolutions in the across range dimensions. The technique of focusing the parabolic antenna is discussed and applied to a 2-1/2 foot parabolic antenna at X-band. The results of the pattern measurements at various ranges from 2.8 m to 5 m are provided.

Wu, L. K.↗
NASA NTRS2011

Scanning and Defocusing Properties of Microstrip Reflectarray Antennas

A symmetric reflectarray, consisting of variable-size square patch elements with a commonly used mathematical model for the horn in the form of a cosine function, has been designed using the transmit mode technique for different f/D ratios with 10 dB edge taper. Subsequently, the antennas were analyzed for the radiation pattern and gain. The infinite array model was used to determine the reflection phase of each patch element in the design and analysis codes. By displacing the feed laterally, the scan characteristics were obtained, such as the beam deviation factor, gain loss, and pattern degradation. The properties of reflect arrays were compared to those of the conventional paraboloidal reflectors. The same procedure was used to study the scan properties of offset reflectarrays. There is no cross-polarized radiation in the principal planes for a symmetric system. Cross-polarized radiation exists in non-principal planes off broadside in symmetric systems, with greater levels for larger values of subtended angles. Such cross-polarized radiation level increases with subtended angle just as cross-polarization level increases with decreasing values of f/D ratios for symmetric paraboloids in non-principal planes. Pattern distortions and gain loss were found to be more severe in the case of a microstrip reflectarray compared to the conventional parabolic reflector. The scan performance of the reflect arrays was found to improve with f/D ratios as is true for paraboloids. In general, scanning by means of displaced feed is limited to a few beam - widths in reflectarrays. Feed displacement in the axial direction of a symmetric reflectarray was investigated and compared to that of paraboloids. The gain loss due to the defocused feed of a reflectarray was found to be nearly the same as that of a paraboloid of the same subtended angle for larger values of f/D, and for displacements away from the antenna. The gain loss of an axially defocused reflectarray was found to be greater than that of a paraboloid for displacements closer to the antenna, especially for smaller values of f/D. In general, the performance of a defocused reflectarray was found to be poorer than that of a comparable paraboloid reflector.

Rengarajan, Sembiam↗
NASA NTRS1973

High performance S-band horn antennas for radiometer use

Horn antennas of four types: pyramidal corrugated, conical corrugated, pyramidal dual mode and conical dual mode, have been constructed and evaluated for use as S-band radiometer antennas. Each of the structures is described and radiation patterns and impedance and resistive loss measurements including a layer of foreign material on a thin radome, are presented. A precision method for determining reflection losses is described using a multiprobe reflectometer technique. The same technique is also applied to the measurement of resistive losses by closing the ends of the antennas with short circuit plates and determining the losses from an accurate measurement of the reflection coefficient. The radiation patterns were recorded with the aid of a real-time digital computer. The stored patterns were then processed to yield gain and beam efficiency. It was concluded that it is possible to design a highly efficient antenna for radiometer use and to measure its parameters precisely. However, it was found that it is necessary to modify the conventional definition of beamwidth somewhat if this term is to be meaningful for radiometer applications.

Caldecott, R.↗
NASA NTRS1974

Sinusoidal reaction formulation for radiation and scattering from conducting surfaces

A piecewise-sinusoidal reaction technique is developed for scattering and radiation from perfectly conducting bodies of arbitrary shape. The theory and numerical results for scattering patterns of rectangular plates and radiation patterns of corner-reflector antennas are presented. Experimental measurements are included for comparison with the calculated data.

Richmond, J. H.↗
NASA NTRS1975

Sinusoidal reaction formulation for radiation and scattering from conducting surfaces

A piecewise-sinusoidal reaction technique is proposed for the study of scattering and radiation from perfectly conducting bodies of arbitrary shape. The reaction technique described is a moment method based on the integral equation of an electric field. A theory of sinusoidal reaction formulation for radiation and scattering problems is outlined, in which the scattered field is obtained by integrating the surface currents. Numerical results are presented for the scattering patterns of rectangular plates and corner reflectors and the radiation patterns of corner-reflector antennas.

Wang, N. N.↗
NASA NTRS1972

Theoretical analyses on Apollo lunar surface electrical properties experiment transmitter antenna.

The purpose of this study is to investigate the characteristics of the transmitter antenna of lunar surface electrical properties experiment. It is desirable to evaluate the current distribution, far-field radiation pattern and input impedance of the transmitter antenna in order to determine the electromagnetic sounding effects from the lunar subsurface. The analysis is based on the treatise of the long wire antenna with passive loadings. Both cases of the antenna placed in free space and in a dissipative medium are taken into consideration.-

Yu, I.-P.↗
NASA NTRS1997

Feasibility Study of Optically Transparent Microstrip Patch Antenna

The paper presents a feasibility study on optically transparent patch antennas with microstrip line and probe feeds. The two antennas operate at 2.3 GHz and 19.5 GHz respectively. They are constructed from a thin sheet of clear polyester with an AgHT-8 optically transparent conductive coating. The experimental results show good radiation patterns and input impedance match. The antennas have potential applications in mobile wireless communications.

Simons, Rainee N.↗
NASA NTRS1997

Feasibility Study of Optically Transparent Microstrip Patch Antenna

The paper presents a feasibility study on optically transparent patch antennas with microstrip line and probe feeds. The two antennas operate at 2.3 GHz and 19.5 GHz respectively. They are constructed from a thin sheet of clear polyester with an AgHT-8 optically transparent conductive coating. The experimental results show good radiation patterns and input impedance match. The antennas have potential applications in mobile wireless communications.

Simons, Rainee N.↗
NASA NTRS2012

Telecommunications Antennas for the Juno Mission to Jupiter

The Juno Mission to Jupiter requires a full sphere of coverage throughout its cruise to and mission at Jupiter. This coverage is accommodated through the use of five (5) antennas; forward facing low gain, medium gain, and high gain antennas, and an aft facing low gain antenna along with an aft mounted low gain antenna with a torus shaped antenna pattern. Three of the antennas (the forward low and medium gain antennas) are classical designs that have been employed on several prior NASA missions. Two of the antennas employ new technology developed to meet the Juno mission requirements. The new technology developed for the low gain with torus shaped radiation pattern represents a significant evolution of the bicone antenna. The high gain antenna employs a specialized surface shaping designed to broaden the antenna's main beam at Ka-band to ease the requirements on the spacecraft's attitude control system.

Vacchione, Joseph D.↗
NASA NTRS1984

Case study of sample spacing in planar near-field measurement of high gain antennas

Far field antenna patterns can be reconstructed from planar near field measurements acquired at a sample spacing of lambda/2 or less. For electrically large antennas, sampling at the Nyquist rate may result in errors due to system electronic drift over long acquisition times. The computer capacity may limit the largest size of the near field data set. The requirement to sample at the Nyquist rate is relaxed for high gain antennas which concentrate most of the radiated energy into a small angular region of the far field. The criteria for sample spacing at greater than lambda/e through the use of a priori information of the antenna radiation characteristics are presented. Far field patterns of a 30 GHz dual offset reflector system with a 2.7 m parabolic main reflector are computed from near field data obtained at sample spacings ranging from 0.1 lambda to 10 lambda. The effects of sampling interval and spectrum cutoff on the far field patterns are discussed.

Acosta, R. J.↗
NASA NTRS1993

Effect of a Dielectric Overlay on a Linearly Tapered Slot Antenna Excited by a Coplanar Waveguide

The effect of a dielectric overlay on a linearly tapered slot antenna (LTSA) is studied. The LTSA under study has very wide bandwidth and excellent radiation patterns. A dielectric overlay improves the patterns and directivity of the antenna by increasing the electrical length and effective aperture of the antenna. A dielectric overlay can also be used to reduce the physical length of the antenna without compromising the pattern quality.

Simons, Rainee N.↗