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Title: Differentially fed active antennas
Author: Sagor, Md. Hasanuzzaman
ISNI:       0000 0004 5360 9178
Awarding Body: University of Greenwich
Current Institution: University of Greenwich
Date of Award: 2014
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The original contribution to knowledge made by this research work is demonstrating the benefits of differentially fed balanced transmit antenna in modern communication system. Extensive experimental studies have established the fact that a true differential amplifier feeding a balanced antenna offers higher linearity and lower distortions compared to the single ended feeding technique, even while using the same amplifier. With continuing advancements in personal communications in this era of digital economy, the demand for wireless connectivity has grown radically, resulting in stringent performance requirement for RF components. Differential circuits are preferred choice in RFIC design due to its good noise immunity and low distortion characteristics. But it is observed that single ended PAs and LNAs are used for the feeding part because of the antenna industry’s tendency to stick to conventional 50Ω interface. Therefore, differentially fed transmit balanced antenna is an area of current research, which has been studied in this thesis. The study was set out with a review of the state-of-the-art in active integrated antennas. Following that, the ground plane influence on antenna radiation pattern was explored and novel techniques to compensate the effects were presented. It was observed that the current flow in a coaxial cable also affects radiation pattern. Hence, a novel method was proposed to measure wireless devices in the anechoic chamber eradicating the need of any cable attachments. Broadband differential amplifiers were then reviewed with a view to feed balanced and unbalanced antennas for demonstrating the potential of differential feeding technique over the conventional one. The amplifier with differential output interface exhibited higher gain and linearity in both bench test and radiated power test. Further improvement in linearity was reported by lowering the output resistance of the amplifier. Afterwards, a broadband antenna with stable radiation pattern and impedance was designed to carry out radiated harmonic measurements, which illustrated that the fully differential output configuration possesses significantly lower harmonic distortion. All these measurement results have suggested that balanced antenna fed by differential amplifier can be the best solution for applications demanding higher output power, greater linearity and lower distortion. Therefore it is recommended to re-evaluate the idea of power amplifier and antenna interface in RF front-end designs.
Supervisor: Callaghan, Peter Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TJ Mechanical engineering and machinery