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Wideband Low-Profile Antenna Arrays: Fundamental Limits and Practical Implementations
Doane, Jonathan P

2013, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Advanced wireless communication and sensing systems have created a growing need for high performance, compact antennas. Low-profile wideband phased arrays are of particular interest, and have recently been shown to be capable of extremely large bandwidths. However, the size, weight, and cost of phased arrays still makes them impractical for many applications. The development of thinner, lightweight, and inexpensive wideband arrays is critical to improving the capabilities of small platforms such as small unmanned aerial vehicles.

Like all antennas, phased arrays are limited by a fundamental compromise between size and performance. Although the theoretical limitations of electrically small antennas have been well known for over 60 years, similarly general limits have not yet been developed for periodic antenna arrays. In the first part of this thesis, we derive a new fundamental bandwidth limit for any periodic array that is backed by a conducting ground plane and constructed from passive and reciprocal materials. This limit is related to several critical design factors, including the array's thickness, polarization, scan angle, materials used, as well as the overall complexity of the array design. We also consider the common case when all radiating currents are confined to a thin planar sheet placed above the ground plane. We show here that such planar phased arrays have a fundamental impedance bandwidth limit of 8.3:1 (with VSWR ≤ 2:1), in the absence of material loading. This bandwidth may be further improved by adding dielectric superstrate or magnetic substrate material layers.

Knowledge of such fundamental bandwidth limits is extremely useful in the design of practical wideband arrays, which is the focus of the second part of this thesis. A key challenge with many wideband arrays is developing a feed circuit that supports extremely wide bandwidths without significantly adding to the size, weight, and cost of the design. Here, we demonstrate a novel approach that overcomes this problem by exploiting the natural reactance of the feed circuit as a simple impedance matching network for the array. The result is a simultaneous reduction in size and weight and improvement in bandwidth compared to other feeding techniques. We refer to our design as the Tightly Coupled Dipole Array with Integrated Balun (TCDA-IB), and it achieves 7.35:1 bandwidth while maintaining a low VSWR of ≤ 2.65:1 while scanning to ± 45° in all planes. A prototype 8×8 array was constructed and demonstrated excellent performance relative to simulation. We also demonstrate that by adding reconfigurable components to the TCDA-IB, its maximum scan angle may by increased to as much as ± 70° while maintaining a 5:1 impedance bandwidth.

Our fundamental bandwidth limits reveal for the first time the extent of the realizable design space for wideband low-profile arrays, and suggest there are significant opportunities for further improvement. Several practical techniques are also presented for increasing bandwidth and scanning performance while reducing the total size, weight and cost of the array. In summary, the ongoing development of high-performance wideband low-profile arrays will likely remain an important and fertile area of research for the foreseeable future.
John Volakis, Dr (Advisor)
Kubilay Sertel, Dr (Advisor)
Chris Baker, Dr (Committee Member)
265 p.

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Doane, J. (2013). Wideband Low-Profile Antenna Arrays: Fundamental Limits and Practical Implementations. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Doane, Jonathan. "Wideband Low-Profile Antenna Arrays: Fundamental Limits and Practical Implementations." Electronic Thesis or Dissertation. Ohio State University, 2013. OhioLINK Electronic Theses and Dissertations Center. 23 Nov 2017.

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Doane, Jonathan "Wideband Low-Profile Antenna Arrays: Fundamental Limits and Practical Implementations." Electronic Thesis or Dissertation. Ohio State University, 2013. https://etd.ohiolink.edu/

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