A laser ionises a filament of air and a metal ring drives it without touching it, producing the first demonstrated transmission from a plasma-filament antenna — at 30 MHz, in the VHF band.
An antenna is a conductor of a particular length. That length sets the frequencies it handles well, which is why a radio telescope looks nothing like a mobile phone and why spacecraft carry antennas that must unfold mechanically after launch. Changing an antenna’s length normally means changing the hardware.
Researchers at North Carolina State University have demonstrated an antenna with no hardware to change. Writing in the IEEE Journal of Microwaves, they report transmitting radio waves from a filament of ionised air drawn by a laser — the first time, they say, that anyone has shown a plasma-filament antenna working.
How a beam of air becomes a conductor
The physics rests on ionisation. A sufficiently intense laser pulse passing through air strips electrons from the molecules along its path, leaving a narrow channel of plasma. Plasma contains free charge carriers, which makes it electrically conductive — and a conductive filament of the right length is, in principle, an antenna.
The practical obstacle has always been how to feed it. A conventional antenna is soldered to a transmission line. There is nothing to solder to a column of glowing air, and putting metal in contact with it would defeat the purpose.
The team’s solution is contactless. A metal ring acts as a capacitor, with the laser passing through its centre. A radio-frequency generator feeds the ring, which produces an electromagnetic field that drives the plasma filament into transmitting — coupling energy into the plasma across empty space, without any physical connection.
That feed arrangement is arguably the real contribution. The conductivity of laser-induced plasma filaments has been understood for years; what has been missing is a way to drive one as an antenna.
What was and was not demonstrated
The paper’s title names the achievement precisely: transmission at 30 MHz, at the bottom edge of the VHF band. The release gives no other figures — no radiated power, no efficiency, no gain, no comparison against a conventional antenna of equivalent length.
Those absences matter for judging the result, and so does one explicit limitation: the team demonstrated transmission but did not test reception. They say the antenna should also work as a receiver, which is a reasonable expectation from antenna reciprocity, but expectation is not demonstration, and reception at useful sensitivity may prove harder — a plasma filament is a noisy, fluctuating conductor, and noise matters far more on the receiving side.
Prya Darshni, a PhD student at NC State and corresponding author of the paper, is clear about where this sits. “This is the first step, but it is a big step,” she said — “it is the first time anyone has ever demonstrated that plasma-filament antennas can work. Now that we’ve shown it is possible, we can begin improving its performance.”
Tunable, steerable, and gone when you want it
The appeal is in what the laser lets you change. “By controlling the parameters of the laser, you can control the characteristics of the plasma filament — including its length,” Darshni said, which means the antenna’s frequency range is set in software rather than in metal. One apparatus could cover bands that would otherwise need several separate antennas.
Direction is adjustable too. “The technique we’ve demonstrated here would allow users to control the angle of the plasma filament antenna via beam steering,” she said — pointing the antenna by pointing the laser, with no moving parts.
Her own description is more evocative than any of this: “The plasma beam antenna looks like a lightsaber and is tunable, meaning we should be able to transmit across a broad range” of frequencies.
There is an implicit feature the release does not dwell on. Switch off the laser and the antenna ceases to exist. For applications where a physical antenna is a liability — because it can be detected, damaged or must survive a launch — an antenna that appears on demand and vanishes afterwards is an unusual proposition.
Why space is the obvious target
Paul Franzon, Cirrus Logic Distinguished Professor of Electrical and Computer Engineering at NC State and a co-author, locates the application. “This is an exciting new concept that enables one to be able to have a customized antenna without complex mechanical deployment mechanisms,” he said.
Deployment mechanisms are a genuine problem in spacecraft engineering. A large antenna must fold to fit a fairing and then unfold reliably in orbit, and deployment failures have ended missions. An antenna that is created by a laser needs no hinges, no motors and no deployment sequence to go wrong.
Franzon also addresses the obvious objection — that space has no air to ionise. “In low earth orbit, there is sufficient air to form a plasma,” he said. The upper atmosphere is extremely thin but not empty, and at low orbital altitudes there is residual gas.
That claim is the one most in need of testing. “Sufficient” is doing a lot of work in a sentence about a medium orders of magnitude less dense than the air in a North Carolina laboratory. Plasma density determines conductivity, and conductivity determines whether the filament radiates usefully. A demonstration at sea level establishes the principle; it says little about performance at 400 kilometres, and the release reports no modelling or vacuum-chamber work on the question.
Documentation
The release credits Darshni as corresponding author, with Franzon and Arthur Dogariu of Texas A&M University and Princeton University as co-authors, Dogariu having assisted with measurements. No funding sources are listed; the conflict-of-interest statement reports none. The paper is open access, published 1 September 2026, with the release following on 5 October.
Plasma antennas have been proposed since at least the 1960s, generally using gas confined in tubes, which gives up the tunability that makes the idea attractive. An unconfined filament drawn in open air keeps it. Whether the radiated power can be brought to a useful level is the question the next few years will answer — but a first demonstration is a first demonstration, and this is one.
Notes
- Darshni, P., et al. “Laser-Induced-Plasma-Filament Antenna Transmitting 30 MHz VHF.” IEEE Journal of Microwaves, 1 September 2026. DOI: 10.1109/JMW.2026.3722433.
- North Carolina State University. “Researchers successfully demonstrate first-ever plasma beam antenna.” EurekAlert!, 5 October 2026. https://www.eurekalert.org/news-releases/1146444.