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Shape Optimization of Low-Profile UWB Body-of-Revolution Monopole Antennas
Zhao, Jing

2011, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.

There is great interest in developing low-profile ultra-wideband (UWB) antennas that operate from low VHF up to several GHz to support high bandwidth communication systems. A concurrent need exists for small size antennas that generate omnidirectional vertically polarized radiation over the horizon. This continued demand for UWB and small size antennas implies significant challenges in radio frequency aperture design. Not surprisingly, this topic has been of strong interest in the research community over the last decade.

This dissertation focuses on the development of novel approaches to systematically design and optimize the shape of a body-of-revolution (BoR) monopole antenna subject to radiation objectives and size constraints. To this end, two types of antennas are proposed following different design philosophies. Specifically, a frequency-scaled inverted-hat antenna (IHA) is first proposed with its outer surface composed of multiple ellipses that follow the growth rate of an exponential spiral. It is demonstrated that controllable input impedance and uniform radiation patterns can be maintained by this design. For the latter property, increasing diffraction from the elliptical curvatures is exploited to achieve a broader radiation pattern at higher frequencies.

A second UWB monopole is proposed by instead following a design optimization approach to construct the outer surface of the antenna. The employed techniques include a random walk for antenna outer profile generation, a genetic algorithm for optimization, and a BoR moment method analysis--all combined in a single design package. The weighted global criterion method is adopted to construct the multi-objective cost function. The minimization of this cost function amounts to minimizing the difference between a potential optimal point and a utopia point that combines separate optimal designs for all key objectives within the solution space. Example designs are presented to demonstrate performance improvements due to antenna shape optimization. In comparison to the original IHAs of the same size, the optimized designs are shown to deliver larger bandwidth, higher gain at low VHF band, and more stable pattern at higher frequencies. Importantly, except for the cost function construction, the design optimization approach requires little prior knowledge in the theory of antennas, making it well suited for exploring a variety of unknown topics in the future. In addition, the matching condition and pattern stability of the optimized monopole can be further improved by means of resistive loading.

Several prototypes of different sizes were fabricated using standard spinning technology and measured from low VHF band up to 2 GHz. These wideband apertures demonstrate the efficacy and accuracy of the novel and low-profile UWB designs.

John L. Volakis, PhD (Advisor)
Chi-Chih Chen, PhD (Committee Member)
Ronald M. Reano, PhD (Committee Member)
Robert J. Burkholder, PhD (Committee Member)
120 p.

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Zhao, J. (2011). Shape Optimization of Low-Profile UWB Body-of-Revolution Monopole Antennas. (Electronic Thesis or Dissertation). Retrieved from

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Zhao, Jing. "Shape Optimization of Low-Profile UWB Body-of-Revolution Monopole Antennas." Electronic Thesis or Dissertation. Ohio State University, 2011. OhioLINK Electronic Theses and Dissertations Center. 21 Sep 2017.

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Zhao, Jing "Shape Optimization of Low-Profile UWB Body-of-Revolution Monopole Antennas." Electronic Thesis or Dissertation. Ohio State University, 2011.


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