Author

Albert Smith

Date of Award

Fall 2018

Document Type

Open Access Thesis

Department

Electrical Engineering

First Advisor

David Matolak

Abstract

With the rise in use of Unmanned Aerial Systems (UAS), there is a need for safe and reliable integration into existing infrastructure. A proposed system for beyond line of sight control links for UAS is a Ku-band air-to-satellite communication system. To ensure this proposed system does not interfere with existing terrestrial infrastructure that operates in the Ku band, an examination of the Ku-band air-to-ground channel is required. The focus of this thesis is the modeling of the Ku-band AG channel. Tests consisting of transmitting a single tone continuous wave signal were conducted with a signal generator onboard NASA’s Viking S-3 aircraft. Transmission was via a custom Ku-band monopole antenna mounted on the bottom of the aircraft’s fuselage. A ground site mimicking existing terrestrial point-to-point infrastructure was used to collect received power measurements. Also included at the ground site were two wider-beamwidth antennas, to enable some assessment of multipath and polarization effects. Measurements were conducted using three inclination (elevation) angles, 0°, 2.5°, and 5°, and the aircraft was flown at three approximately constant-altitudes. The channel characteristic that was measured was attenuation, also termed path loss. Path loss estimates were made using free-space and two- ray models, and these models were refined by the inclusion of atmospheric refraction, attenuation due to fog, and curved earth models for the various flight geometries. These models were further refined by assessing angular offsets to the antenna gain patterns, as the aircraft transmitter gain patterns had deep nulls that affected measured power as the aircraft pitch varied both up and down during test flights. Measured data was then also fit

to a log-distance model for each flight test. These log-distance models are commonly used for terrestrial settings and provide a measure of goodness of fit. Overall, path loss exponents are close to the value of 2, as expected; this is the value for a free-space channel. Log-distance models yielded standard deviations in the range of 1.68 to 5.13 dB. When the inclination angle of the receiver was 5°, the measured fit equation for co-polarized antennas was found to have a path loss exponent very close to that of free-space, but as inclination angles decreased (closer to the horizon boresight), path loss exponents increased.

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