Optically transparent antennas for multi-modal sensing

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Silva, Zachary J.
Valenta, Christopher R.
Durgin, Gregory D.
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The advent of multi-modal data fusion, the rise of CubeSats, and the dawn of the drone, among others, have all put pressure on sensor developers to increase payload performance while decreasing their size, weight, and power (SWAP). RF-EO/IR fusion enables enhanced situational awareness due to the changes in material properties at different electromagnetic frequencies. The research explores high performance optically transparent conductors realized as antennas used for single aperture RF-EO/IR sensor fusion. The trade-off between optical transparency and conductivity is apparent and well documented within the materials science community. The fundamental principles to achieve optical transparency of a conductor at radio-frequency (RF), microwave, and millimeter wave frequencies, however, has not been well established. The presentation describes transparent conducting oxides in terms of the electromagnetic material properties based on Maxwell’s equations, which exposes potential limits to the simultaneous conductivity at RF and transparency in the optical region. Optical transmittance and imaging measurements to characterize the degradation of the optical system performance are also presented to compare the transparent conductors over an optical aperture, a requirement for single aperture multi-modal sensing. In addition, a new figure of merit for transparent RF conductors is presented which enables the transparent conducting oxides and mesh conductors to be compared directly as a criterion to determine the highest performing optically transparent conductor for RF applications. The figure of merit for transparent RF conductors reveals the mesh is the highest performing material for single aperture multi-modal sensing, but the effects of a mesh conductor in microstrip circuits have not yet been entirely explored in literature. The initial studies have shown that the introduction of mesh alters the effective inductance and capacitance of the transmission line at RF due to its geometry. Methods to predict and compensate for the changes in response due to the mesh are presented to minimize undesired reflections in RF circuitry. In addition, the effects of the mesh are presented to discuss how the mesh conductor affects the radiation properties of a microstrip patch antenna. The research lays the foundation for the design and implementation of an optically transparent phased array antenna which can be utilized in future applications for single aperture multi-modal sensing.
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