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Miniaturized, Inherently Matched, and Scalable Folded Dipole Antennas with Applications in Narrowband Sensing
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- Author / Creator
- Das, Sanghamitro
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This work presents a novel technique for miniaturizing folded dipole antennas using a simple series reactive loading scheme that enables the input impedance to be engineered, such that the antenna can be matched inherently to either a real or a complex source impedance at a specified level of miniaturization. This ability to achieve good matching with respect to an essentially arbitrary source impedance allows these miniaturized antennas to be integrated into various wireless systems without using an external matching network, which usually increases the overall size and complexity.
First, the well-known analytical model of an unloaded folded dipole antenna is extended to include the effects of reactive loading. Initially, a symmetric loading scheme is chosen, where it has been shown that in order to realize good matching conditions, an extremely large loading inductance and an extremely small loading capacitance will be necessary. However, if asymmetries are introduced in the loading scheme, the required loading values can become much smaller and more easily realizable.
The conclusions from this study are then applied in order to realize a practical example, where a printed folded dipole antenna is miniaturized to 25% of its resonant length by employing a fully asymmetric loading scheme, i.e., one arm of the antenna is made inductive and the other is made capacitive, and excellent matching is achieved with respect to a selected source impedance. The widths of the folded dipole arms are also made unequal in order to use as an additional degree of freedom. A unique feed structure is also designed to provide a balanced input to the antenna. It is shown that any effects from this feed or other practical losses can be compensated easily by adjusting the loading reactance values. Furthermore, it is found that the miniaturized folded dipole antenna has a radiation efficiency that is comparable to that of an equivalent loaded conventional dipole antenna, however by virtue of being inherently matched (and therefore not requiring a potentially lossy and bulky external matching network), the folded dipole antenna exhibits a better realized gain, and hence a higher radiated power. The antenna is fabricated and experimental results are found to be in excellent agreement with the simulated.
Finally, the applicability of this miniaturization technique is studied for narrowband electrically small sensor antennas. A 75% miniaturized fully printed folded dipole prototype is designed for matching to a real source impedance at the UHF ISM frequency band (902-928 MHz) specified for sensing applications in North America. In the next step, the input-impedance engineering technique is extended to match an equally miniaturized folded dipole antenna to a complex source impedance, and its suitability as a RFID tag antenna is discussed. Once again, excellent agreement is found between the measured and simulated results for both designs. -
- Graduation date
- Fall 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.