8 research outputs found

    The Impedance of a Loop Near a Conducting Half-Space

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    The change in complex impedance between an ideal one-turn circular coil located above and parallel to a conducting half-space with respect to a similar isolated coil has been calculated. From this result a series expansion of the integrand allows the solution to be approximated by terms expressed as complete elliptic integrals. Results have been calculated for the change in impedance as a function of the lift-off distance and the conductivity of the half-space for a coil of representative.radius

    Experimental Demonstration of Microwave Signal/Electric Thruster Plasma Interaction Effects

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    An experiment was designed and conducted in the Electric Propulsion Laboratory of NASA Lewis Research Center to assess the impact of ion thruster exhaust plasma plume on electromagnetic signal propagation. A microwave transmission experiment was set up inside the propulsion test bed using a pair of broadband horn antennas and a 30 cm 2.3 kW ion thruster. Frequency of signal propagation covered from 6.5 to 18 GHz range. The stainless steel test bed when enclosed can be depressurized to simulate a near vacuum environment. A pulsed CW system with gating hardware was utilized to eliminate multiple chamber reflections from the test signal. Microwave signal was transmitted and received between the two hours when the thruster was operating at a given power level in such a way that the signal propagation path crossed directly through the plume volume. Signal attenuation and phase shift due to the plume was measured for the entire frequency band. Results for this worst case configuration simulation indicate that the effects of the ion thruster plume on microwave signals is a negligible attenuation (within 0.15 dB) and a small phase shift (within 8 deg.). This paper describes the detailed experiment and presents some of the results

    Antenna Near-Field Probe Station Scanner

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    A miniaturized antenna system is characterized non-destructively through the use of a scanner that measures its near-field radiated power performance. When taking measurements, the scanner can be moved linearly along the x, y and z axis, as well as rotationally relative to the antenna. The data obtained from the characterization are processed to determine the far-field properties of the system and to optimize the system. Each antenna is excited using a probe station system while a scanning probe scans the space above the antenna to measure the near field signals. Upon completion of the scan, the near-field patterns are transformed into far-field patterns. Along with taking data, this system also allows for extensive graphing and analysis of both the near-field and far-field data. The details of the probe station as well as the procedures for setting up a test, conducting a test, and analyzing the resulting data are also described

    Acoustic simulation of airframe mounted conical spiral antenna

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    The radiation coverage of circularly polarized electromagnetic antennas mounted on complex aerodynamic bodies were simulated by ultrasonic simulation technique. Special acoustic transducers were used to simulate the hemispherical radiation pattern of conical spiral antennas, and were mounted on 22.6 wavelength scaled down ultrasonic models of Bomarc and BQM-34A airframes for simulation work. [...]Electrical and Computer Engineering, Department o

    Experimental Results of the Impact of an Ion Thruster Plasma on Microwave Propagation

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    Electric thrusters are being considered for a variety of space missions because of the significant propellant savings that result from the use of high performance, electric propulsion technologies, Propellant mass savings reduces spacecraft launch requirements and increases mission lifetime and payload. The impact of electric thruster plasma plumes on microwave signal propagation however is an important spacecraft integration concern. Arcjets were the first electric thrusters to be considered for operational missions. Ling, et al., studied the effect of arcjet plumes on propagation. Arcjets produce a lightly ionized plume and Ling's analysis predicted that the plume would have a negligible effect on communication. Plumes from the higher performance ion thrusters being developed exhibit higher ionization levels, plasma temperatures and particle velo@ities than arcjets. Therefore, there was a need to assess the impact due to these plumes. To address this need, the authors designed and performed a series of experiments to examine propagation effects of plumes. The challenge with these experiments was that they had to be performed in the operational environment of the thruster. Therefore, the experiments were conducted inside a metal chamber which could be depressurized to simulate a near vacuum condition of space. The metal chamber presents a potential large source of error to the propagation measurements due to the corruption of the desired data by multiple wall reflections within the chamber. This chamber effect was minimized by employing a pulsed-continuous wave transmitter and receiver system. This system, based on an HP8510 Network Analyzer, uses external hardware time gating to eliminate the clutter of the spurious reflections. Additionally, high gain antennas were used in the measurements to ensure that minimal amounts of energy ",ere transmitted/received in undesirable directions. The measurements took place in Vacuum Facility 5 of the Electric Propulsion Laboratory at the NASA Glenn Research Center. This facility utilizes a cylindrical, stainless steel, vacuum chamber, which is 18.3 m long and 4.6 m in diameter. For the tests being described here a 30 cm diameter, xenon ion thruster was used. The thruster provided between 500 W and 2.3 kW of operating power. The thruster was mounted on a stand along the axis of the chamber near one of its ends

    An Overview of the Antenna Measurement Facilities at the NASA Glenn Research Center

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    For the past twenty years, the NASA Glenn Research Center (formerly Lewis Research Center) in Cleveland, Ohio, has developed and maintained facilities for the evaluation of antennas. This effort has been in support of the work being done at the center in the research and development of space communication systems. The wide variety of antennas that have been considered for these systems resulted in a need for several types of antenna ranges at the Glenn Research Center. Four ranges, which are part of the Microwave Systems Laboratory, are the responsibility of the staff of the Applied RF Technology Branch. A general description of these ranges is provided in this paper

    Respiratory Tract and Mediastinum

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