Transparent antennas are a new class of radiator in which both the conductive radiator and the supporting dielectric are optically clear, so the whole device can be mounted on glass, plastic, or even the display of a smart-phone without visually blocking what is behind it. The key idea is to replace the opaque copper patch with a material that is still electrically conductive but also transmits most of the visible-light spectrum, and to place that film on an equally transparent substrate. In practice the antenna is built in the same planar geometries—patch, slot, monopole, loop, fractal or array—as an ordinary printed antenna, yet the physics that governs its behaviour is more complicated because the “transparent conductor” is always a compromise between sheet resistance and optical transmission.
The first design decision is the choice of the transparent conductor. Three families are normally considered.
- Transparent conductive oxides (TCOs), the oldest and most mature, are doped metal-oxide films such as indium-tin-oxide (ITO), fluorine-doped tin-oxide (FTO) or aluminium-/gallium-doped zinc-oxide (AZO/GZO). ITO gives 80–90 % transmission in the visible range and a sheet resistance of 5–20 Ω sq⁻¹ for a 180–300 nm film, values that are adequate for microwave and low-millimetre-wave bands.
