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Beamforming Techniques for the Frequency Diverse Array
Youssef, Yazan
Youssef, Yazan
Date
2020-05
Author
Advisor
Type
Thesis
Degree
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Description
A Master of Science thesis in Electrical Engineering by Yazan Youssef entitled, “Beamforming Techniques for The Frequency Diverse Array”, submitted in May 2020. Thesis advisors are Dr. Hasan Mir and Dr. Lutfi Albasha. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).
Abstract
One of the primary advantages of using a system that employs multiple antennas is the ability to perform spatial beamforming, wherein a phase shift is applied across each of the antenna elements in order to electronically steer the transmitted signal in a desired direction. This architecture is known as a phased array, and much work has been done in order to determine the optimal configuration of the phase shifts that yield a beampattern that exhibits a narrow mainlobe and low sidelobe levels, thus ensuring that the radiated signal is concentrated in the desired direction. However, a phased array is limited in providing control over the beampattern in the angle domain only. Recently, a novel multiple antenna architecture known as the frequency diverse array (FDA) was proposed in which a phase shift and a frequency shift is applied across each of the antenna elements. The beampattern that arises from such an architecture exhibits a dependence on angle, range, and time. Due to the time dependence, existing methods for FDA beamforming will only illuminate a desired spatial location at a specific moment in time. To overcome this problem, a solution has recently been proposed wherein a subarray based FDA receiver architecture consisting of a series of mixers and filters is used in order to perform what is termed as equivalent transmit beamforming. This thesis further develops the equivalent transmit beamforming paradigm at the FDA receiver with a novel and simplified method for achieving a time-invariant beampattern that illuminates the desired spatial location. To reduce the dimensionality of the optimization problem, a fixed form of the frequency offset is proposed based on a novel recursive frequency increment structure. The problem of determining the array weight coefficients in order to steer the array sensitivity to a desired spatial location is formulated as a convex optimization problem that can be easily solved using interior-point methods. Comprehensive simulation results show that the proposed architecture exhibits a beampattern with sidelobe levels comparable to existing methods but with a mainlobe width that has been reduced by nearly an order of magnitude.