If you think about it, an antenna is nothing more than a radio frequency energy sensor, or — more precisely — a transducer. So, it shouldn’t be a surprise that there could be different ways to sense RF that would work as an antenna. A recent paper in Applied Physics Letters explains an atomic antenna comprised of a rubidium vapor cell.
The interesting thing is that the antenna has no electrical components in the antenna, and can be located far away from the actual receiver. Instead of coax cables, the signal is read with a laser.
The experiment uses a 780 nm laser and a 480 nm laser to illuminate the sensor, which contains a corner reflector. The returned laser light changes based on the input signal at the antenna. That means, in theory, you could locate the antenna far away on a tower or mountaintop since the laser and sensing equipment don’t need to be close. The experiments had the sensor 10 m to 30 m away from the base station, but we’d imagine it would be possible to bridge larger gaps with some modifications.
The RF in question was in the 16 GHz – 20 GHz range. Unsurprisingly, the antenna cell is small, measuring 150 mm by 27 mm. The rubidium doesn’t require special temperatures. The lasers, too, aren’t anything unusual, producing just a few dozen milliwatts on each beam.