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  • AERODYNAMICS
  • COMMUNICATIONS AND RADAR
  • GENERAL
  • 1995-1999  (36)
  • 1
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    Dielectric property measurements in the Electromagnetic Properties Measurement Laboratory (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The capability to measure the dielectric properties of various materials has been developed in the Electromagnetic Properties Measurement Laboratory (EPML) of the Electromagnetics Research Branch (ERB). Two measurement techniques which have been implemented in the EPML to characterize materials are the dielectric probe and waveguide techniques. Several materials, including some for which the dielectric properties are well known, have been measured in an attempt to establish the capabilities of the EPML in determining dielectric properties. Brief descriptions of the two techniques are presented in this report, along with representative results obtained during these measurements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-110147 , NAS 1.15:110147
    Format: application/pdf
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  • 2
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    The Deep Space Network stability analyzer (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A stability analyzer for testing NASA Deep Space Network installations during flight radio science experiments is described. The stability analyzer provides realtime measurements of signal properties of general experimental interest: power, phase, and amplitude spectra; Allan deviation; and time series of amplitude, phase shift, and differential phase shift. Input ports are provided for up to four 100 MHz frequency standards and eight baseband analog (greater than 100 kHz bandwidth) signals. Test results indicate the following upper bounds to noise floors when operating on 100 MHz signals: -145 dBc/Hz for phase noise spectrum further than 200 Hz from carrier, 2.5 x 10(exp -15) (tau =1 second) and 1.5 x 10(exp -17) (tau =1000 seconds) for Allan deviation, and 1 x 10(exp -4) degrees for 1-second averages of phase deviation. Four copies of the stability analyzer have been produced, plus one transportable unit for use at non-NASA observatories.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Goddard Space Flight Center, The 26th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 221-233
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  • 3
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    Minimal trellises for linear block codes and their duals (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We consider the problem of finding a trellis for a linear block code that minimizes one or more measures of trellis complexity for a fixed permutation of the code. We examine constraints on trellises, including relationships between the minimal trellis of a code and that of the dual code. We identify the primitive structures that can appear in a minimal trellis and relate this to those for the minimal trellis of the dual code.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 148-158
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  • 4
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    Trellis complexity bounds for decoding linear block codes (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We consider the problem of finding a trellis for a linear block code that minimizes one or more measures of trellis complexity. The domain of optimization may be different permutations of the same code or different codes with the same parameters. Constraints on trellises, including relationships between the minimal trellis of a code and that of the dual code, are used to derive bounds on complexity. We define a partial ordering on trellises: If a trellis is optimum with respect to this partial ordering, if has the desirable property that it simultaneously minimizes all of the complexity measures examined. We examine properties of such optimal trellises and give examples of optimal permutations of codes, most notably the (48,24,12) quadratic residue code.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 159-172
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  • 5
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    Arbitrarily shaped dual-stacked patch antennas: A hybrid FEM simulation (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A dual-stacked patch antenna is analyzed using a hybrid finite element - boundary integral (FE-BI) method. The metallic patches of the antenna are modeled as perfectly electric conducting (PEC) plates stacked on top of two different dielectric layers. The antenna patches may be of any shape and the lower patch is fed by a coaxial cable from underneath the ground plane or by an aperture coupled microstrip line. The ability of the hybrid FEM technique for the stacked patch antenna characterization will be stressed, and the EM coupling mechanism is also discussed with the aid of the computed near field patterns around the patches.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Simulation of Thin Slot Spirals and Dual Circular Patch Antennas Using the Finite Element Method with Mixed Elements; p 58-76
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  • 6
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    Performance of an artificial absorber for truncating FEM meshes (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: We investigate the effectiveness of an artificial absorber for truncating finite element (FE) meshes. Specifically, we present the implementation of a novel mesh truncation approach using a perfectly matched anisotropic absorber for waveguides and stripline circuits. This truncation scheme is useful in many applications, including antennas, scattering, and microwave circuits.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Simulation of Thin Slot Spirals and Dual Circular Patch Antennas Using the Finite Element Method with Mixed Elements; p 77-87
    Format: text
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  • 7
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    Design considerations for an archimedean slot spiral antenna (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: The design goal is to develop a 118-157 MHz, vertically polarized, low-profile (or conformal) antenna as a replacement for VHF AM blade antennas on aircraft. This design is to be arrived at by scaling the dimensions of an antenna designed for a center frequency of 1.1 GHz. The design prior to scaling may have the following maximum dimensions: diameter less than 3.70 in. and thickness less than 0.50 in. Although a four-arm spiral design was originally suggested, a two-arm spiral may also be used, as both mode-1 and mode-2 (sum and difference) radiation patterns aren't required. While a four-arm spiral can easily be designed should both sum and difference patterns be required, the two-arm design will provide the required sum pattern and simplify the design problem somewhat: only one feed is required, and the feed area geometry is more straightforward. Polarization requirements dictate that a slot spiral be used, as opposed to a wire spiral. Two similar radiating structures were considered. The first is the standard archimedean spiral antenna. The second is a hollow archimedean spiral antenna, essentially a standard archimedean spiral with the inner portion removed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Simulation of Thin Slot Spirals and Dual Circular Patch Antennas Using the Finite Element Method with Mixed Elements; p 21-46
    Format: text
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  • 8
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    An efficient and accurate model of the coax cable feeding structure for FEM simulations (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: An efficient and accurate coax cable feed model is proposed for microstrip or cavity-backed patch antennas in the context of a hybrid finite element method (FEM). A TEM mode at the cavity-cable junction is assumed for the FEM truncation and system excitation. Of importance in this implementation is that the cavity unknowns are related to the model fields by enforcing an equipotential condition rather than field continuity. This scheme proved quite accurate and may be applied to other decomposed systems as a connectivity constraint. Comparisons of our predictions with input impedance measurements are presented and demonstrate the substantially improved accuracy of the proposed model.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Simulation of Thin Slot Spirals and Dual Circular Patch Antennas Using the Finite Element Method with Mixed Elements; p 47-57
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  • 9
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    Slot spiral antenna modeling using hybrid/mixed FE-BI technique (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: This report is concerned with the numerical simulation of the printed slot spiral antenna (SSA) using the finite element - boundary integral (FE-BI) analysis. It has been reported that the FE-BI technique is suited for modeling microstrip patch antennas of any shape, printed on layered planar structure or cylindrical platform and fed with a coaxial cable or a microstripline network underneath the radiating elements. However, direct application of the hybrid FE-BI technique to thin slot spirals requires excessive sampling rates to accurately simulate the geometry. To alleviate the meshing/modeling difficulties encountered with cavity-backed slot antennas, we describe a mixed finite element-boundary integral formulation. As in the past, the boundary integral is used to describe the radiation of the slot above the cavity. However the cavity is now modeled using a suitable mix of edge and node elements. The latter are used only at the aperture of the thin slot so that the nodes follow the center line of the slot. In this manner, regular size elements can be used regardless of the slot's width and any meshing restrictions are substantially relaxed. The proposed mixed element FE-BI formulation introduces three different computational regions and as expected this complicates the generation of the discrete system.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Simulation of Thin Slot Spirals and Dual Circular Patch Antennas Using the Finite Element Method with Mixed Elements; p 1-20
    Format: text
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  • 10
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    A novel photonic oscillator (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We report a novel oscillator for photonic RF systems. This oscillator is capable of generating high-frequency signals up to 70 GHz in both electrical and optical domains and is a special voltage-controlled oscillator with an optical output port. It can be used to make a phase-locked loop (PLL) and perform all functions that a PLL is capable of for photonic systems. It can be synchronized to a reference source by means of optical injection locking, electrical injection locking, and PLL. It can also be self-phase locked and self-injection locked to generate a high-stability photonic RF reference. Its applications include high-frequency reference regeneration and distribution, high-gain frequency multiplication, comb-frequecy and square-wave generation, carrier recovery, and clock recovery. We anticipate that such photonic voltage-controlled oscillators (VCOs) will be as important to photonic RF systems as electrical VCOs are to electrical RF systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 32-43
    Format: application/pdf
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