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Article Dans Une Revue AIP Advances Année : 2017

Mesh parameters influence on transparent and active antennas performance at microwaves

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Optically transparent and active square loop coplanar antennas operating in X-band are investigated in this letter. The frequency tunability is provided by a surface mounted beam-lead varactor with micrometric size, thereby no-visible to the naked eye. The influence of the metal mesh parameters on the sheet resistance (from 0.05 Ω/sq to 0.54 Ω/sq), the optical transparency (from 66% to 89%) and the microwave performance (return loss, resonance frequency, radiation pattern and gain) of such antennas is evaluated, compared with those of an opaque counterpart, and finally discussed. This study paves the way of their promising implementation on new surfaces, namely building and car windows for future wireless communications systems. © 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license Nowadays the development of wireless communications and wireless sensors requires emerging technologies to enhance the communication network performance, especially in dense urban areas. An attractive possibility concerns the development of optically transparent antennas to improve their location in the cities by accessing new surfaces, namely glazed surfaces such as building and car windows. These antennas can be elaborated from transparent and conducting layers printed on such glass substrates. The most usual material belongs to the transparent and conducting oxide (TCO) family, namely indium tin oxide (ITO). 1–5 Hybrid solutions based on TCO materials and ultrathin metal films are also available 6–10 such as ITO/metal/ITO multilayers 11 or AgHT films (ITO/silver multilayers printed on polyester substrates). 12,13 Nevertheless the related ohmic loss and skin depth loss at microwaves are restrictive for antenna applications. In addition, optical transparency depends on the wavelength value in the visible light spectrum due to interference fringes. Moreover ITO is based on a critical raw material, namely indium. An alternative solution has been developed specifically in our Laboratory. It is based on micro-metric mesh metal films printed on glass substrates. 14 Metal layers exhibit low sheet resistance (and low ohmic loss as a result) and apertures inside the metal layers give the needed and constant optical transparency in the visible light spectrum (no interference fringes). Metal thickness adjustment prevents any skin depth effect at the operating frequency without affecting the optical transparency level. 14 Optically transparent passive antennas have already been developed from such a material at various frequencies, 15–18 thereby demonstrating the full relevance of this new technology. Now the main challenge consists in making such transparent antennas active, i.e. being tunable in terms of operating frequency 19,20 while keeping up a high level of optical transparency and microwave performance. For this purpose, a surface mounted beam-lead varactor with micrometric size has been used and implemented on such antennas to provide frequency tunability without changing their overall transparency. 21 This tunability is relevant in X-band for radar or satellite communication applications. The present work focuses on the mesh parameters influence on the active antenna performance in terms of sheet resistance value in DC mode, optical transparency in the visible light spectrum a Electronic mail: xavier.castel@univ-rennes1.fr 2158-3226/2017/7(8)/085120/8 7, 085120-1
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hal-01577675 , version 1 (27-04-2018)

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Alexis Martin, Xavier Castel, Mohamed Himdi, Olivier Lafond. Mesh parameters influence on transparent and active antennas performance at microwaves. AIP Advances, 2017, 7 (8), pp.085120. ⟨10.1063/1.4985746⟩. ⟨hal-01577675⟩
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