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Novel Implementations of Wideband Tightly Coupled Dipole Arrays for Wide-Angle Scanning
Yetisir, Ersin

2015, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Ultra-wideband (UWB) antennas and arrays are essential for high data rate communications and for addressing spectrum congestion. Tightly coupled dipole arrays (TCDAs) are of particular interest due to their low-profile, bandwidth and scanning range. But existing UWB (>3:1 bandwidth) arrays still suffer from limited scanning, particularly at angles beyond 45° from broadside. Almost all previous wideband TCDAs have employed dielectric layers above the antenna aperture to improve scanning while maintaining impedance bandwidth. But even so, these UWB arrays have been limited to no more than 60° away from broadside.
In this work, we propose to replace the dielectric superstrate with frequency selective surfaces (FSS). In effect, the FSS is used to create an effective dielectric layer placed over the antenna array. FSS also enables anisotropic responses and more design freedom than conventional isotropic dielectric substrates. Another important aspect of the FSS is its ease of fabrication and low weight, both critical for mobile platforms (e.g. unmanned air vehicles), especially at lower microwave frequencies. Specifically, it can be fabricated using standard printed circuit technology and integrated on a single board with active radiating elements and feed lines.
In addition to the FSS superstrate, a modified version of the stripline-based folded Marchand balun is presented. As usual the balun serves to match the 50-Ohm coaxial cable to the high input impedance (~200-Ohm) at the terminals of array elements. Doing so, earlier Wilkinson power dividers, which degrade efficiency during E-plane scanning, are eliminated. To verify the proposed array concept, 12x12 TCDA prototype was fabricated using the modified balun and the new FSS superstrate layer. The design and experimental data showed an impedance bandwidth of 6.1:1 with VSWR<3.2. The latter VSWR was achieved even when scanning down to ±60° in the H-plane, ±70° in the D-plane and ±75° in the E-plane. All array components, including the FSS, radiating dipoles and the feed lines are placed on the same PCB, vertically oriented over the array ground plane, resulting in a low-cost and light-weight structure.
The effects of finite aperture sizes in presence of FSS or dielectric superstrates are also considered. Specifically, we compare the performance of finite TCDAs with FSS or dielectric loading. The performance metric is beam pointing accuracy for moderate array sizes (~30dBi gain) with various edge element terminations. It is shown that even terminating two unit cells at the array edges can provide effective suppression of edge-born waves and achieve excellent beam accuracy. This is the case when both the FSS elements and radiating dipoles are resistively loaded in the unit-cells along the aperture edges.
John L. Volakis, Prof (Advisor)
Nima Ghalichechian, Dr (Committee Member)
Chi-Chih Chen, Dr (Committee Member)
Fernando L. Teixeira, Prof (Committee Member)

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Yetisir, E. (2015). Novel Implementations of Wideband Tightly Coupled Dipole Arrays for Wide-Angle Scanning. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Yetisir, Ersin. "Novel Implementations of Wideband Tightly Coupled Dipole Arrays for Wide-Angle Scanning." Electronic Thesis or Dissertation. Ohio State University, 2015. OhioLINK Electronic Theses and Dissertations Center. 21 Sep 2017.

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Yetisir, Ersin "Novel Implementations of Wideband Tightly Coupled Dipole Arrays for Wide-Angle Scanning." Electronic Thesis or Dissertation. Ohio State University, 2015. https://etd.ohiolink.edu/

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