| Summary: | An on-glass optically transparent monopole antenna with ultrawide bandwidth is presented in this work, and the proposed antenna is of ring shape and coplanar waveguide fed structure. Optically transparent indium tin oxide (ITO) thin film with a thickness of <inline-formula> <math display="inline"> <semantics> <mrow> <mo>~</mo> <mn>160</mn> <mrow> <mo> </mo> <mi>nm</mi> </mrow> </mrow> </semantics> </math> </inline-formula> is used as the conductive layer, which is sputtered on an optically transparent glass substrate. An impedance bandwidth of 6 GHz from 1 to 7 GHz is achieved, with a return loss lower than −10 dB, meaning a fractional bandwidth of 150%. The proposed antenna exhibits reasonable radiations of omni-directionality in the H plane and bi-directionality in the E plane. Like other transparent antennas discussed in literature, the antenna gain is relatively low (−4 dBi at 5 GHz). In order to optimize the antenna performance, multi-film approach is proposed to reduce its sheet resistance, and the result shows that the antenna gain at 4 GHz can be improved from −8 dBi to 5 dBi when optimizing the sheet resistance from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>10</mn> <mrow> <mo> </mo> <mi mathvariant="sans-serif">Ω</mi> </mrow> <mo>/</mo> <mi>sq</mi> </mrow> </semantics> </math> </inline-formula> to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.01</mn> <mrow> <mo> </mo> <mi mathvariant="sans-serif">Ω</mi> </mrow> <mo>/</mo> <mi>sq</mi> </mrow> </semantics> </math> </inline-formula>. The designed antenna possesses a high optical transparency, which makes it easy to integrate to the surface of windows or display panels, and it can be applied for solar energy harvesting and many other ultra-wideband applications, with little chance of detection.
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