Browsing by Author "Tsai, Y. -L."

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A Reconfigurable Antenna System Consisting of Post-wall E-plane Horns
(2010-01-01)
Hwang, R. -B.
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Yen, H. -Y.
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Yang, C. -S.
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Chin, C. -Y.
;
Tsai, Y. -L.
In this article, we report a reconfigure antenna that is able to radiate different topologies of radiation pattern. Such an antenna system is composed of a four-way power divider made from a cavity-type structure fabricated using printed circuit technology. Due to the symmetric electric field distribution in the resonant cavity, the power divider maintains equal amplitude- and phase- distribution in the frequency range from 2.3 GHz to 2.5 GHz. Moreover, the high isolation among there ports was obtained. The output ports of the four-way power splitter respectively go through four radio frequency switches connected to four E-plane horn antennas. Notably, the four E-plane horns are integrated in a metallic parallel-plate structure equipped with four flared open ends. To enhance the isolation among the four E-plane horns, the metallic cylinders array is employed as a sidewall of the horn antenna. Moreover, prior to connecting to each horn antenna the signal is connected to a radio frequency switch to turn on (to the antenna) or off (to a terminator). Therefore, we can dynamically switch the beam among the four sectors. Specifically, the beam pattern covering several sectors can also be obtained. In addition to the numerical simulation of the overall antenna structure, we have fabricated this antenna and measured its radiation characteristics. The excellent agreement is obtained between the measured and simulated results.
Towards High-Efficiency Triple-Junction Solar Cells with Bio-Inspired Nanostructures
(2013)
Yu, Peichen
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Han, H. -V.
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Yang, T. -T.
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Hung, M. -M.
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Hong, C. -Y.
Triple-junction solar cells offer extremely high power conversion efficiency with minimal semiconductor material usage, and hence are promising for large-scale electricity generation. To fully exploit the broad absorption range, antireflective schemes based on biomimetic nanostructures become very appealing due to sub-wavelength scale features that can collectively function as a graded refractive index (GRIN) medium to photons. The structures are generally fabricated with a single-type dielectric material which guarantees both optical design robustness and mechanical durability under concentrated illumination. However, surface recombination and current matching issues arising from patterning still challenge the realization of biomimetic nanostructures on a few micrometer thick epitaxial layers for MJSCs. In this presentation, bio-inspired antireflective structures based on silicon nitride (SiNx) and titanium dioxide (TiO2) materials are demonstrated on monolithically grown Ga0.5In0.5P/In0.01Ga0.99As/Ge triple-junction solar cells. The nano-fabrication employs scalable polystyrene nanosphere lithography, followed by inductively-coupled-plasma reactive-ion-etching (ICP-RIE). We show that the fabricated devices exhibit omni-directional enhancement of photocurrent and power conversion efficiency, offering a viable solution to concentrated illumination with large angles of incidence. Moreover, a comprehensive design scheme is also presented to tailor the reflectance spectrum of sub-wavelength structures for maximum photocurrent output of tandem cells.