Plasma Antenna | Hacker News Reader

Plasma Antenna

en.wikipedia.org

136 pointsbcaa7f3a8bbc54 comments

Had a dig around for some pictures of such antennas and found this: https://www.researchgate.net/figure/A-model-4068-MHz-ac-plas...

Find myself wishing such tech was prevalent during the early days of mobile phones and massive external aerials, but that's just the inner Jedi in me.

Imagine a Sci-Fi title with this scene: At the last moment, some critical battlefield information is transmitted by a huge, bright and colorful beam of plasma antenna that shines the ground like Sun at night. It would make a spectacular and impressive scene of SFX and CGI, just like the SFX of the wrapped engine in the new Star Trek..

> during the early days of mobile phones

Probably not a good idea, in its original form, it requires a lot of power from the mains to maintain its arc discharge, which is what turns it into an antenna, kind of like a vacuum tube that needs a constant heating power. But Wikipedia says antenna-on-chip is possible, which is quite interesting.

Early mobile phones were car-mounted. So if you had a nuclear-powered car a plasma antenna would fit right in.

And a tube transmitter, of course!

The picture does not look like arc discharge, it's more like fluorescent lamp.

A fluorescent lamp is a mercury-vapor gas discharge lamp with a phosphor coating. Doesn't that qualify as an arc discharge?

And you literally need a thousand volts to kickstart a fluorescent lamp, at least on decent tubes.

Let me pull up my "flyback transformer on a chip".

No.

An arc discharge is a hot, high current density process. [1] The discharge in a fluorescent lamp is a glow discharge: low current density, moderate temperature and extended volume. [2]

[1] https://en.wikipedia.org/wiki/Electric_arc [2] https://en.wikipedia.org/wiki/Glow_discharge

The first article gives fluorescent lights as an example of modern usage of arc lighting... The second article distinguishes between glow discharge and arcing.

One of my university lecturers, John Rayner, worked on developing these back in the day. Managed to track down a paper he published on it which is quite interesting: https://ieeexplore.ieee.org/document/1291644

Does anyone know how stealth fighter aircraft are able to incorporate radar hardware that doesn't act like a giant retro reflector? Putting a radar array on the front of a stealth fighter just seems like painting a giant bullseye on it, even if it's not emitting.

I wonder if something like this could already be in use, since it becomes invisible to radar as soon as the plasma generator is turned off?

I'm not exactly versed in the subject, but going off of a recent class on wireless transmissions, perhaps they instead use lots of small transmitters/receivers along the hull and rely on post processing to piece that together.

I've never worked on stealth aircraft, but energy has to travel from the transmitter, through the aircraft's radar cover, off the array itself, then get back through the cover and back to the receiver.

There are probably ways to filter for specific RF frequencies on the cover so only those in specific bands can get through, then the array itself might absorb some portion of the energy that gets through. The array also might be at an angle so waves are reflected in a different direction, or there might be radar absorbing material placed in specific spots that helps minimize reflections. I think the arrangement of elements in the phased array itself could also lead to reduced RCS at certain angles. Again these are just educated guesses, I would imagine the details are classified.

https://aviation.stackexchange.com/questions/25368/how-are-a...

Going further with the idea it could be possible to make an antenna from ionized air.

As it turns out someone already patented "Antenna of ionized air": https://patents.google.com/patent/US2760055 The patent expired in 1973.

Meteor burst communications

https://en.wikipedia.org/wiki/Meteor_burst_communications

Meteors punch ion trails through the atmosphere that serve as antennas for various purposes.

People frequently build these with Tesla coils. People also build plasma speakers, which is similar in concept.

https://youtu.be/JH-YmzZgZ-Q

It ought to be a lot easier to make this work, nowadays, with a hard-ultraviolet laser. Tune it just by pointing at something the right distance away.

I'm not antenna knowledgeable nor plasma knowledgeable.

Is there a layman's explanation about what the advantages / why there are advantages here?

It talks about turning off the plasma antenna, is that any different than simply not using a regular antenna? ... or what they mean by stealth or "resistance to electronic warfare and cyber attack".

I guess with a metal antennae you have a permanently reflective surface, AIUI once one of these are disabled they become basically radio-transparent again, which means less of a blip on radar

It also means they don't receive when off, which renders them resistant to some forms of electronic warfare.

Normally antennae are constructed out of solid materials. The plasma is controlled by electricity, so the gain characteristics can be rapidly controlled and dynamically tuned in real-time (possibly).

So, like the ultimate SDR?

It's related, but not the same. SDR happen after you received your signal, where you can, in software, pick different ways of decoding the signal.

This, however lets you dynamically choose the antenna length, and each frequency has a perfect length that works best for it.

So the two are complimentary, but at different parts of the process.

Right so it's like SDA - a software defined antenna

Hard-wired antennas can be detected by their shadows and reflections in the RF bands. Additionally, unless they are hardened against it, extreme RF energy, as might be generated by an EMP or by a highly-directional attacking antenna, can damage circuits connected to the receiving antenna.

When the plasma antenna is turned off, it stops existing. There's nothing there to attack or detect.

A possible future advantage would be shaping the plasma with magnetic fields, to create customizable antenna geometries, or geometries that electrically extend beyond the physical bounds of the equipment. Imagine using a laser small enough to fit in a backpack to create a 1/4 wave antenna long enough to transmit or receive at 30 kHz, with length 2.5 km .

You could create a plasma antenna 2500m long, send a message to a submarine 150 m below the surface, then it just disappears when you turn it off.

Thank you.

What a cool visual. Setting up a small beacon like object on the ground, standing back a couple hundred feet, and then a beam of bright blue light bursts several kilometers into the air, sending a quick burst of data while the capacitors powering it can keep it alive.

If using multiple converging lasers, the antenna need not be connected to the equipment. Two lasers could ionize the air in a line 2500m long, and a third could excite the center of it in a modulated fashion. That would be transmit only, unless you had some way to measure the energy levels at that center point from a distance.

It would be unlikely to glow brightly enough in the visual spectrum to see in the daytime, but it would be pretty cool at night.

For normal people... pretty much nothing. You need power to keep the plasma hot, it's a safety hazard, and it's not cheap. For electrically-small antennas it looks like it might be slightly more efficient than a wire antenna of the same size (or slightly smaller than a wire antenna of the same efficiency) but most of the advantages listed pertain to military applications, and that seems to be who's driving the research.

It is said it could be used for 60ghz wifi (wisig)

>> For normal people... pretty much nothing.

Did you even read the article? They mention Solid State Plasma antennas, which can be fabricated using standard silicon chip fabrication techniques.

It's tunable for one, and it might be very fast to tune. At very high frequencies these are targeting (>50ghz), making an antenna suitably wideband to cover the entire bandwidth of some service is difficult and might result in a compromised antenna.

For security applications, the ability to turn it off is kind of nice; no antenna = no backscatter. OTOH how stealthy can a plasma antenna be when it is on?

Slightly OT, but there was no image in the page, so I scrolled down to the bottom and clicked a link in the "See also" section labeled "Article with image". The article had no image of a plasma antenna. What gives, Wikipedia?

The picture was there [0], but later livescience.com updated the website and it's gone due to link rotting. Even worse, archive.org didn't have the image archived (but the "zoom picture" text can be seen). Wikipedia is one of the most affected website by link rotting.

What gives, the Web? Donate to archive.org today!

[0] https://web.archive.org/web/20081010224347/http://www.livesc...

Another article [0] (2007) featuring the image.

[0] http://www.nbcnews.com/id/22113395/ns/technology_and_science...

EDIT: Presentation from Igor Alexeff and Theodore Anderson (University of Tennessee):

https://www.ysc.org.ua/2011/data/i.alexeff_presentation.pdf

I’m betting this will have horrible noise temperature. Not good for receiving.

Did you really read it ?

> At satellite frequencies, they exhibit much less thermal noise and are capable of faster data rates.

Yes I did. This is the main presentation from the reference web site.

http://nebula.wsimg.com/d0cadaec2cf44c9682cebb1610ce1a91?Acc...

If you look at the thermal analysis, it is incomplete. They are only considering the thermal noise of the reflector. The noise temperature of an antenna is a function of temperature AND aperture efficiency, with the latter set by the conductivity of the reflector. Plasma is not a great conductor (compared to metal), as is shown by the nested antennas. High performance satcom (e.g. NASA DSN) not only cool the electronics, they cool the feeds also.

There is another paper where they show a tube covering a LNB. Looks like some BS. I don’t see any actual measurements of noise temperature (which are very easy to do).

http://nebula.wsimg.com/48f10bd80f702313a1d8d094fc7d6b01?Acc...

I didn’t see any of the papers published in IEEE APS.

I design antennas for a living, and this sets my BS detector off, and it did 10 years ago too. They look fine for TX (the patterns look good), but the noise data is conspicuously absent.

Here is another noise analysis, but again it is incomplete. Just show some measurements.

http://nebula.wsimg.com/754ac5460a5e1531953c79dd1c4863b7?Acc...

I thought plasma was a near-perfect conductor... Is that wrong?

You don't need high temperature for plasma; just low pressure. There is a big difference between glow discharge and arc discharge.

If you look at plasma attenuation of a reentry body, it’s about 30 dB. Even a thin sheet of foil or perforated screen is way more (> 100 dB).

They just need to hook an antenna to a spectrum analyzer (with low noise path) and measure the noise density. If it is anywhere slightly above -174 dBm/Hz, then it is not going to function well as a satcom antenna.

That picture they show of the tube taped onto the LNB feed, they say it “intercepted” the signal. Do they mean it blocked it? Sure, it will if the plasma is conductive enough, but it should also drop the noise coming out of the receiver. Maybe it swamped the receiver with noise. Can’t tell. If they can pattern the lower frequency antennas, they can certainly take the time to do some noise measurements.

Maybe the issue is exciting the plasma, and that is noisy. I’d think you couldn’t do it with pulse excitation unless you limited the rise time. You could do it with CW, say a magnetron, way outside your operating band.

Can someone wire one to a guitar and pair it with a rydberg vapour cell as the recieving antenna, so the audiophile community can finally have something to justify their pricing.

https://aip.scitation.org/doi/10.1063/1.5099036

On the other end we have : https://en.wikipedia.org/wiki/Plasma_speaker

Good call. Since they demonstrated 2 channel already, maybe drive that with a standard electric guitar and then have a Tesla coil driven by a bass.

People just do it with Tesla coils https://youtu.be/JH-YmzZgZ-Q

The Gamechanger Audio Plasma pedal uses a plasma arc tube to generate overdrive. It's kind of gimmicky, but also ridiculously cool - it's inherently noise gating, because the arc extinguishes at low signal levels.

https://www.gamechangeraudio.com/plasma/

Fascinating!

Did not know you could make an antenna out of a plasma; this is fascinating; thank you for expanding what I thought was possible!

Your microwave has a plasma antenna in it - it makes microwaves. It’s called a magnetron

Or a gyrotron if you eat really big hot pockets.

Technologies like this suddenly make a lot of science fiction seem outdated. :)

people interested in this may also be interested in GDD Gas Discharge Detectors, they can also be used for mixing / heterodyning

Wow, a gas discharge mixer! I couldn't believe it exists...

I think I have seen projects using miniature neon indicator lamps tubes as GDD's / mixers

I have often toyed with the idea of making oscilloscopes, and spectrum analyzers with them, but that would take a long time to explain...

Also, I miswrote it's Glow Discharge Detector

Another idea is repurpousing plasma display panels as a grid of GDD detectors, as an imaging array.

For an example circuit using a neon indicator lamp see figure 1 of the 2010 article:

http://www.academia.edu/download/44461415/Heterodyne_Detecti...

This 2016 article measures the light emitted from the neon indicator lamp instead (with FMCW scheme to detect distance as well)

https://www.osapublishing.org/viewmedia.cfm?uri=prj-4-6-306&...

This setup improves response time (bandwidth) of the output signal.

Reply on news.ycombinator.com