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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. / Ph. D.

A data acquisition and control system (DACS) has been designed and constructed for use during propagation experiments with the OLYMPUS satellite. OLYMPUS is a European Space Agency experimental satellite that broadcasts coherent at 12, 20 and 30 GHz and is viewed from Blacksburg, Virginia at an elevation angle of 13.9°. This low elevation angle yields a relatively long atmospheric path which serves to accentuate propagation effects. The DACS is a custom design which collects propagation, environmental and status information and periodically calibrates external equipment. Beacon signal strength is measured via a hybrid analog/digital receiver. The analog portion the receiver utilizes the coherency of the satellite beacons to track 20 and 30 GHz signals to the noise floor. The digital portion of the receiver is contained within the DACS and consists of a stand-alone microprocessor which filters the beacon signal to determine the power in a 3 Hz bandwidth. Additional DACS circuitry collects analog and digital input channels and controls external through digital output channels. Digital outputs are used to reference the collected to known by performing periodic calibrations on external equipment. Analog input channels are used to measure quantities including external temperature, wind speed wind direction, while digital inputs monitor alarm conditions. The VIEW program utility permits an operator to graphically view data in real time. In addition, collected data is stored to tape without an interruption in data collection. DACS operation has been virtually continuous since data collection was started on August 3, 1990. / Master of Science