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  • 1
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    Analysis of finite phased arrays of circular microstrip patches (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A method is presented for analyzing a finite planar array of circular microstrip patches fed by coaxial probes. The self- and mutual impedances between array elements are calculated using the method of moments with the dyadic Green's function for a dielectric layer on a ground plane. The patch circuits are determined by using the reaction integral equation. The active input impedance as well as the active element pattern of the array are computed from a knowledge of the resultant patch currents. The calculated results for two-element and eight-element linear arrays are in good agreement with experimental data. The active reflection coefficient and element pattern for the center and edge elements of a two-dimensional array as a function of scan angle are also presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 37; 1355-136
    Format: text
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  • 2
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    Analysis of elliptical and circular microstrip antennas using moment method (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A method of calculating the input impedance of either a circular or a slightly elliptical microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Green's function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 954-959
    Format: text
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  • 3
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    The 15-meter antenna performance optimization using an interdisciplinary approach (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A 15-meter diameter deployable antenna has been built and is being used as an experimental test system with which to develop interdisciplinary controls, structures, and electromagnetics technology for large space antennas. The program objective is to study interdisciplinary issues important in optimizing large space antenna performance for a variety of potential users. The 15-meter antenna utilizes a hoop column structural concept with a gold-plated molybdenum mesh reflector. One feature of the design is the use of adjustable control cables to improve the paraboloid reflector shape. Manual adjustment of the cords after initial deployment improved surface smoothness relative to the build accuracy from 0.140 in. RMS to 0.070 in. Preliminary structural dynamics tests and near-field electromagnetic tests were made. The antenna is now being modified for further testing. Modifications include addition of a precise motorized control cord adjustment system to make the reflector surface smoother and an adaptive feed for electronic compensation of reflector surface distortions. Although the previous test results show good agreement between calculated and measured values, additional work is needed to study modelling limits for each discipline, evaluate the potential of adaptive feed compensation, and study closed-loop control performance in a dynamic environment.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Jet Propulsion Lab., Proceedings of the Mobile Satellite Conference; p 465-470
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  • 4
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    An analysis technique for microstrip antennas (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The paper presents a combined numerical and empirical approach to the analysis of microstrip antennas over a wide range of frequencies. The method involves representing the antenna by a fine wire grid immersed in a dielectric medium and then using Richmond's reaction formulation (1974) to evaluate the piecewise sinusoidal currents on the grid segments. The calculated results are then modified to account for the finite dielectric discontinuity. The method is applied to round and square microstrip antennas.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation; AP-25; Nov. 197
    Format: text
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  • 5
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    A novel method of calculating far-field patterns of large aperture antennas (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A method is described for calculation of the radiation pattern of large aperture antennas. A piece-wise linear approximation of the aperture field using overlapping pyramidal basis functions allows the radiation pattern of an aperture antenna to be calculated as though it were a two-dimensional array. The calculation of radiation pattern data versus theta and phi, suitable for 3-D or contour plot algorithms, is achieved by locating the array in the yz-plane and performing a summation over the aperture field data sampled on a square grid. A FORTRAN subroutine is provided for performing radiation pattern calculations. Numerical results are included to demonstrate the accuracy and convergence of the method. These numerical results indicate that typical accuracies of + or - 0.1 dB for Directivity, + or - dB for the 1st Sidelobe Level, and + - 2dB for the 2nd Sidelobe Level can be obtained with an aperture grid of 45x45 points and requires approximately 0.02 seconds CPU time per far-field data point on a VAX 11/750 with a floating point accelerator.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87644 , NAS 1.15:87644
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  • 6
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    Feed System Design Considerations for Large Space Antenna Systems. Part 1: Multiple Apertures with Non-overlapping Feeds (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: A feed system design for large space antenna systems was considered. A multiple aperture system with nonoverlapping feeds is examined. Circular and quadrant aperture reflector radiation patterns are compared and the effect of adjacent aperture on radiation patterns of multiple aperture reflector antennas is illustrated. The following systems are examined: (1) feed design optimization for a multiple aperture reflector antenna; (2) radiation pattern for two quadrant reflector with optimized feed design; (3) multiple beam concept utliizing apertures and nonoverlapping feeds; (4) beam contours for two quadrant of multiple beam multiple aperture concept; (5) superposition of beams from two quadrants of multiple beam multiple aperture concent; (6)compensation for mislalignment of interleaved beams from two quadrants; and (7) beam quality improvement due to reorienting feed for offset reflector.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Large Space Antenna Systems Technol., 1984, Pt. 2; p 693-702
    Format: text
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  • 7
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    Efficient detection of a CW signal with a linear frequency drift (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An efficient method is presented for the detection of a continuous wave (CW) signal with a frequency drift that is linear in time. Signals of this type occur in transmissions between any two locations that are accelerating relative to one another, e.g., transmissions from the Voyager spacecraft. We assume that both the frequency and the drift are unknown. We also assume that the signal is weak compared to the Gaussian noise. The signal is partitioned into subsequences whose discrete Fourier transforms provide a sequence of instantaneous spectra at equal time intervals. These spectra are then accumulated with a shift that is proportional to time. When the shift is equal to the frequency drift, the signal to noise ratio increases and detection occurs. Here, we show how to compute these accumulations for many shifts in an efficient manner using a variety of Fast Fourier Transformations (FFT). Computing time is proportional to L log L where L is the length of the time series.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-188900 , NAS 1.26:188900 , RIACS-TR-89-51
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  • 8
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    Electronic compensation for reflector surface distortion to improve radiation pattern characteristics of antennas (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A simple procedure is described for determining the excitation coefficients of an array feed which compensates for the surface distortion of a reflector antenna to improve the radiation pattern in such a way as to approximate the performance of the undistorted antenna. A computer simulation for a practical feed array is presented as an example of compensation for the distortion of an actual antenna.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-100652 , NAS 1.15:100652
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  • 9
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    Resonant frequency of microstrip antennas calculated from TE-excitation of an infinite strip embedded in a grounded dielectric slab (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The calculation of currents induced by a plane wave normally incident upon an infinite strip embedded in a grounded dielectric slab is used to infer the resonant width (or frequency) of rectangular microstrip antennas. By placing the strip inside the dielectric, the effect of a dielectric cover of the same material as the substrate can be included in the calculation of resonant frequency. A comparison with measured results indicated agreement of 1 percent or better for rectangular microstrip antennas constructed on Teflon-fiberglass substrate.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-80190
    Format: application/pdf
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  • 10
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    CWG: A FORTRAN program for mutual coupling in a planar array of circular waveguide-fed apertures (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A FORTRAN program which calculates the mutual coupling between circular apertures in a conductive plane is documented. The program is quite general in that the apertures do not have to be the same sizes, nor do they have to be polarized in the same direction. In addition, several waveguide modes (TE and/or TM) may be specified in the apertures and the mutual coupling between all combinations of apertures and modes will be calculated. The program also allows multiple layers of homogeneous dielectrics to be placed over the aperture array. Outside the layered region, one can specify either a homogeneous half-space, or a perfect reflecting surface.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-101614 , NAS 1.15:101614
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