Browsing by Author "Allnutt, Richard Mallory"

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    Small scale antenna diversity as a means of reducing the effects of multipath fading for handheld satellite communications systems
    Allnutt, Richard Mallory (Virginia Tech, 1995-11-03)
    This document discusses the measurements conducted at Virginia Tech, in Blacksburg, VA, and at COMSAT Labs, in Clarksburg MD, to determine the impact of multipath fading upon a circularly polarized L-Band satellite-to-handheld communications system using an omni-directional antenna. A significant finding was that motion of the satellite could induce fades of up to lOdB, well in excess of the small link margins available to satellite-to-handheld systems (typically ≤ 3dB). A method for ameliorating multi path fading was then sought. It was also found that the multipath fading effect was significantly different at as small a distance as half a wavelength from the original antenna position. Multipath signals could actually combine at the new position to form a small increase in signal to noise ratio (S/N), rather than a fade of as much as 16dB. Therefore it was determined that a small-scale antenna diversity system might offer a solution to the problem of multipath fading.
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    Total power radiometers at 12, 20 and 30 GHz used in the OLYMPUS experiment at Virginia Tech
    Allnutt, Richard Mallory (Virginia Tech, 1991-06-12)
    This paper discusses the total power radiometers in the propagation experiment at Virginia Tech using the OLYMPUS communications satellite. The experiment is set up to measure the received signal strength of beacons at 12.502, 19.770 and 29.656 GHz on board the OL YMPUS satellite in order to gather space-earth propagation statistics for a period of one year. The radiometers are used to set the clear sky reference levels for the beacon receivers. The paper begins with an overview of radio signal attenuation mechanisms, and a general discussion of radiometry. A description of the OLYMPUS radiometers follows, with sections on calibration techniques and the methods required to convert radiometer data into derived path attenuation for use in setting the clear air reference levels for the beacon receivers. Several novel techniques were used in the Virginia Tech radiometers including the use of voltage to frequency converters for integration purposes, and reference load calibration using a waveguide switch to swap the radiometer input from the antenna to a waveguide load of known and stable temperature. The penultimate chapter contains data recorded in the course of the experiment which was selected at random from the month of January 1991. The data is compared to corresponding free space beacon attenuation data and shows conclusively that the total power radiometer can produce highly accurate and stable attenuation measurements for extended periods of time.