Alvelo Rivera, Enrique M.

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    Design of a polarization adaptive beamforming transmitter sub-array for beyond line of sight satellite communications in unmanned aircraft systems
    (2018-05) Alvelo Rivera, Enrique M.; Medina Sánchez, Rafael H.; College of Engineering; Colom Ustáriz, José; Cruz Pol, Sandra; Rodríguez Solís, Rafael A.; Department of Electrical and Computer Engineering; Padilla, Ingrid Y.
    The market outlook for upgrade, expansion and new acquisition of military UAS equipment exhibits substantial potential to grow during the 10 year period extending from year to year . Some of the mission characteristics and requirements that will drive future UAS development include: continuing microminiaturization, sensor fusion, command, control & communications standardization, and infrastructure integration to achieve smaller, less costly and more capable UAVs. Hence, an increased market demand for research & development of UAS antenna systems is also expected during the same 10 year period. The University of Puerto Rico at Mayagüez is currently developing a “Hybrid Mechanical/ Electronic Steerable Antenna Array for SATCOM Terminals” to help enable significant efficiency and endurance improvements in future UAS platforms. The thesis “Design of a Polarization Adaptive Beamforming Transmitter Sub-Array for Beyond Line of Sight Satellite Communications in Unmanned Aircraft Systems” presented in this document complements the development project of the “Hybrid Mechanical/ Electronic Steerable Antenna Array for Terminals” that will operate in the extended Ku – band frequency range. Furthermore, the “Design of a Polarization Adaptive Beamforming Transmitter Sub-Array for Beyond Line of Sight Satellite Communications in Unmanned Aircraft Systems” provides a fundamental unit cell that enables the development of a beamformer network module that minimizes risks of fabrication errors, simplifies operation & maintenance tasks and provides roll-out flexibility for future antenna system expansions. The microwave circuit included in the “Design of a Polarization Adaptive Beamforming Transmitter Sub-Array for Beyond Line of Sight Satellite Communications in Unmanned Aircraft Systems” consists of one driver amplifier, one 1:2 coupler, two variable phase shifters, one hybrid coupler and two power amplifiers interconnected by microstrip line structures. Simultaneous one dimensional electronic beam steering and polarization tilt rotation might be achieved by electronically adapting the phase shifts provided by both transmission paths to help mitigate the effects of adjacent satellite interference. According to simulation results the overall performance of the “Design of a Polarization Adaptive Beamforming Transmitter Sub-Array for Beyond Line of Sight Satellite Communications in Unmanned Aircraft Systems” meets relevant requirements of key commercial, military and industrial standard specifications available to the general public as unclassified or declassified information. However, it was observed that the predicted polarization axial ratio performance partially complies with MIL-STD-188- 164B standard specifications regarding amplitude variations of the transmission uplink function and linear polarization axial ratio for Ku-band systems using antennas with diameters smaller or equal to . The highest extent of polarization axial ratio degradation was observed at the interconnection between the output ports of the phase shifters and the input ports of the hybrid coupler. The theoretical model developed as part of this research project confirmed that the polarization axial ratio performance suffers severe degradation mainly caused by the introduction of amplitude errors. Hence, variable attenuators were presented as the most practical solution to enable the required amplitude compensation to mitigate the effects of amplitude errors on gain ripple and polarization axial ratio performance.