How to design antenna below 1khz with antenna design software like HFSS? - Page 1
Forum section: electronics / rf-microwave

author: youta556
author_rank: Contributor
timestamp: April 21, 2022, 07:17:22 pm
content: Usually,HFSS,antenna magus can help to design antenna above 1khz.What can be used to design antenna below 1khz?

author: cdev
author_rank: Super Contributor
timestamp: April 21, 2022, 07:52:49 pm
content: Well, you may be able to use NEC, or something similar, (I don't know) but your antenna is going to be very large, very very large. Youre going to have to face that fact.As far as software, with some limitations, (propagation effects) you may be able to simply scale the proportions of the various elements for the lower frequency. As said elsewhere, get ready for large size.Do you have a fairly large plot of land (or a small to medium sized country) to site it on?

author: Bud
author_rank: Super Contributor
timestamp: April 21, 2022, 08:07:17 pm
content: You already have two of them, with built-in directional tracking. They are called ears.

author: TimFox
author_rank: Super Contributor
timestamp: April 21, 2022, 08:14:30 pm
content: The US Navy maintains a very expensive radio transmitter (NAA) operating at 24.0 kHz, formerly 17.8 kHz, with 2 MW power.https://en.wikipedia.org/wiki/VLF_Transmitter_CutlerThe use case is communication with submerged submarines (not very deep).The antenna takes up roughly a square mile.

author: MarkMLl
author_rank: Frequent Contributor
timestamp: April 21, 2022, 08:18:14 pm
content: Quote from: cdev on April 21, 2022, 07:52:49 pmAnd I have to ask why OP insists on yelling at us with print which is both large and emboldened.MarkMLl

author: cdev
author_rank: Super Contributor
timestamp: April 21, 2022, 09:25:03 pm
content: I hope you see that I am trying to be reasonable. After all we're all here to learn. An antenna that is anything even remotely efficient at 1 Khz ia going to be large. Really large. Consider that light travels 186000 miles per second. So, a quarter wavelengh monopole is 1/4 of that!Maybe you could use the mythical space elevator as your monopole? If its made of graphene and carbon nanotubes, they are conductive. So that might work. If you could get it to be an acceptable impedance. And then match to it. Sounds a bit like the problem of using a big tree in the tropics as a HF antenna..So, how would 1Khz signals propagate? Quite some time ago I helped build a database that stored info about the science of things like this. Its still in service and quite useful for such speculation Consulting that it seems that VLF signals are very unlike HF signals and interact with the Earth and itsmagnetospherein a great many ways. .

author: max-bit
author_rank: Frequent Contributor
timestamp: April 22, 2022, 09:45:35 am
content: With such low frequencies, not only the size of the antenna is a problem, but also the interference from the power grid.For such a "huge" antenna, you not only need a lot of space, but also a significant distance from all buildings.

author: coppercone2
author_rank: Super Contributor
timestamp: April 22, 2022, 05:00:23 pm
content: I would say you are not able to build this antenna because of environmental and financial reasons. The only reasonable way to get this long a emitter is to use the earth.https://en.wikipedia.org/wiki/Ground_dipoleThere might be privately funded oil company or mineral company exploratory antennas made like this that run at frequencies near 1KHz. Maybe with the oil problems its not a bad idea to try to get government approval for a organization to research this.. but IMO just get more solar panels instead of fiending for oil.The only reasonably low cost way to try to make a conductor that long is to try to make a partnership with whoever might own a rail road and modify that to make like a loop antenna out of steel, but its still not easy since its not a good conductor and the skin depth of these frequencies means you can't just flash plate copper on stuff. Even with a good antenna you would need a substantial power plant...I wonder what you could do with the earths molten core in a few thousand years when we can maybe dig down there.I also suspect that since this is useful for nuclear war and also oil (which many seem to blame as a cause of the major wars in the last 30 years), that simulators are highly proprietary and guarded if they exist. People want their oil contracts and submarines to be safe. the movie "there will be blood" comes to mind in regards to oil industry having a "private security apparatus" protecting it (its seriously greasy)https://en.wikipedia.org/wiki/Ultra_low_frequencyAnother way to make an actual antenna for this might be to use a extremely powerful laser shot into space so that it ionizes air and makes a conductive path.. but I am not sure how powerful that would need to be, or if you can make such a long conductor easily without blooming.https://ieeexplore.ieee.org/document/9647683more like JJ abrams lol. TLDR : It says to like shoot a rocket that makes a exhaust stream that is then ionized with a laser to reduce laser power requirement.. so you only need a still day, a rocket and a big laser. This is refereed to as an 'ionization channel'.https://www.sto.nato.int/publications/AGARD/AGARD-CP-529/AGARDCP529.pdfHere is a treatise on low frequencies in general.

author: TheMG
author_rank: Frequent Contributor
timestamp: April 22, 2022, 06:45:55 pm
content: Quote from: TimFox on April 21, 2022, 08:14:30 pmFound a very interesting presentation about that:https://limarc.org/wp-content/uploads/2020/04/VLF-Presentation.pdfVery impressive antenna system needed to achieve 74.9% radiation efficiency at these frequencies! Would likely cost BILLIONS to build something like that from scratch nowadays.Now imagine the challenges at 1kHz, a whole order of magnitude lower in frequency! Any antenna that you can make for such low frequency without significant real estate and deep deep pockets is going to be very very inefficient. If you're putting out 1000W transmitter power and getting even 0.1W EIRP out of it at 1kHz, you're doing amazing!!!

author: cdev
author_rank: Super Contributor
timestamp: April 23, 2022, 08:11:43 pm
content: Quote from: Bud on April 21, 2022, 08:07:17 pmThis is very interesting stuff to know about. The Earth rings with VLF. Its not man-made. Its natural.

author: TimFox
author_rank: Super Contributor
timestamp: April 23, 2022, 08:22:33 pm
content: Quote from: cdev on April 23, 2022, 08:11:43 pmI have no experience with 1 kHz EMF into ears, but there is an interesting effect found in high-field MRI magnets.The fluid in the inner ear is conductive, and will feel magnetohydronamic force when the head moves inside a 15 or 20 kGauss DC field.Unfortunately, the signal from that effect to the brain is inappropriate for the human balance mechanism, and the result can be serious nausea or vertigo.

author: cdev
author_rank: Super Contributor
timestamp: April 23, 2022, 08:28:27 pm
content: Just found on Google. Animals that sense Earth's magnetic field include sea turtles, birds, fish and lobsters. Sea turtles, for example, can use the ability for navigation to return to the beach where they were born"Salmon too have an ability to find the streams where they were born and travel up them. This makes sense as a survival strategy.Never underestimate Nature.I have seen (relatively) big salmon attempting to travel up really tiny "streams". Its really something to see.Animals' magnetic 'sixth' sense may come from bacteriaThe question is one that has been unresolved despite 50 years of research!https://www.sciencedaily.com/releases/2020/09/200914112224.htm

author: hagster
author_rank: Frequent Contributor
timestamp: April 23, 2022, 09:26:32 pm
content: The OP asks about designing a 1khz antenna not building one. I see no reason HFSS, NEC, OpenEMS other tool can not be used to design such an antenna.

author: cdev
author_rank: Super Contributor
timestamp: April 24, 2022, 02:05:41 am
content: No reason not agreed. Think big!

author: RoV
author_rank: Regular Contributor
timestamp: April 24, 2022, 01:07:55 pm
content: a transmit antenna is hard, but a receive one is well feasible: take a ferrite cylinder (as large as you can) and wind many turns. Then resonate it and apply to a low noise amplifier.Regarding the question of HFSS or similar: as long as you avoid nonlinear materials, I suppose you could do the design at e.g. 1 MHz and then scale it.

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2022, 03:55:43 pm
content: www.vlf.ithas good low frequency antenna designs

author: TimFox
author_rank: Super Contributor
timestamp: April 24, 2022, 04:47:44 pm
content: Quote from: coppercone2 on April 24, 2022, 03:55:43 pmOne posting therehttp://www.vlf.it/sos-enattos/sosenattos_live.htmlis about sensing magnetic fields at extremely low frequencies (< 100 Hz, down to < 1 Hz), but I don't think that the sensors qualify as "antennas", which respond to radiated waves. Rather, they are "coils" that respond to oscillating magnetic fields that are not radiating.

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2022, 05:04:08 pm
content: I figure on earth they are synonymous with antennas when frequency is low enough, but you are right that for 1KHz which is 300km, you can get into far field on earth (but can you because of the curvature? horizon is 20 miles, so you would need to know how they propagate)Also it needs to be said to be careful with low frequency transmitters, because power lines communications use them (if you did manage to make something (styropyro laser antenna?, careful that the electric company does not confiscate death star)).https://en.wikipedia.org/wiki/Power-line_communication#Long_haul,_low_frequency

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2022, 06:13:25 pm
content: Well it might be space related, there is no reason why a satellite cant unfurl a long dipole or something. No one said its terrestrial. Might be a good materials test to help encourage development of a space elevator.

author: A.Z.
author_rank: Super Contributor
timestamp: April 25, 2022, 11:53:40 am
content: and then, also seehttp://www.grahn-spezialantennen.de/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2022, 02:17:23 pm
content: Not really anything to design, it's fractional wavelength, electrically short -- just make a loop as big as you can afford, then match that to 50 ohms or whatever with a suitable transformer, or coupled loop, or matching network. Make it resonant to get higher gain at very narrow bandwidth, or ignore the reactance to get very low gain (and radiation resistance) over whatever bandwidth you like.Conductor size: also as much as you can afford. Litz an option (pretty coarse at these frequencies, a bundle/multiconductor cable of stranded wire would do quite nicely). Reduces electrical resistance, making radiation resistance a larger part of the total (so, increasing SNR; but still much, much smaller than reactance, unless you tune it out).Use balanced designs, or shielding, to give immunity from local fields (typically of the opposite type, i.e. an inductive loop with E-field immunity, or electrically-short dipole with H-field immunity).Tim

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2022, 03:07:30 pm
content: As pointed out above, with very, very short antennas the series reactance is much higher than the radiation resistance and needs to be tuned out. Unfortunately, with practicable loading coils the ESR of the coil will still be mucy higher than the small radiation resistance and the resulting SNR will suffer.

author: A.Z.
author_rank: Super Contributor
timestamp: April 27, 2022, 07:31:01 pm
content: Quote from: TimFox on April 25, 2022, 03:07:30 pmstill you can build a ferrite sticks loop which, with the help of a tuning cap will allow to go pretty down in frequency, while retaining a manageable size; an example of such a VLF antenna is herehttp://www.vlf.it/etna/etna_live.htmlnot easy to put together, but doesn't require several acres of land, either; then, by the way, the antenna is just one component of the receive chain, it's important, sure, but if what comes next isn't up to the task...

author: geggi1
author_rank: Frequent Contributor
timestamp: April 27, 2022, 09:17:47 pm
content: What are you trying to do with the antenna is the most important question.If i where playing with antennas for these low frequencies I would start building something and then when its start to work test the design with a antenna sim software.Most likely there will be factors not implemented in these softwares that is relevant for low frequeicies.On these low frequencies you will have to make some kind of loop to keep the cost and size at a sensable level.If the atenna is going to be used for reception things can be a bit simpler than for transmision.By using a ferrous material (ferrite and powder iron cores) you can reduce the size of the antenna a lot.The premability material of the core will be the factor reducing the size and number of turns of the loop compared to a air core. You can probably start to look at the types of core material used in switch mode power supplies or RFI prevention at low frequencies.The efficancy of the antenna will be low, but that can be compansated by using more gain in the reception equipment. Look at how its done on VLF reception and earth reception with high gain instrument opamps and sound cards.For transmition you should probably start to look in to electro magnetics and transformers.The simplest rout for this is probably to make a reasonable large multi turn loop tuned with a bank of switched capacitors.If you manage to get the impedanse of the antenna to be in the range of 4-8 ohms you can use a audio amp as the transmisioon aplifier.For gnerating signals for the transmision there are a lot of digi mode ham software that can be usable. The same is also relevant for reception.Modes like WSPR and FT8 is a good place to start with software.

author: MarkMLl
author_rank: Frequent Contributor
timestamp: April 29, 2022, 10:45:06 am
content: Quote from: A.Z. on April 27, 2022, 07:31:01 pmI was wondering whether a ferrite rod or manageable loop would do the job, but was reluctant to comment lest OP's mention of Antenna Magus implied that he had his heart set on an E-field design.At a somewhat higher frequency, buthttp://www.creative-science.org.uk/MSF3.html(and related pages) might be worth mentioning.MarkMLl

author: cdev
author_rank: Super Contributor
timestamp: May 01, 2022, 03:31:57 pm
content: I have some 20 cm x 1 cm ferrite rods that I bought some time ago from a Ukraine seller on ebay.Intended for this purpose, These make fine LF antennas. Just as-is. With a couple of turns of enameled wire around it. They pick up all sorts of stuff. Ive also used a wooden clothes hanger that I have had for years that I used to use for drying laundry in the bathtub before I owned a dedicated "dryer"If one wraps a very few (even just three or four) turns of wire around it it makes a substantial sized loop. Thats what matters. The space that is enclosed. It can be used as a magnetic loop for HF with a variable capacitor. Ive also used a wooden palatte which some fencing material came on as a big loop. It makes a huge armature for wiring of any kind. Placed on its side it made a good ( square) directional loop. A very good HF antenna.Which could likely be moved down in frequency to whatever one needed with some decent variable capacitors. The large size means that it woud capture a lot of signal. My experience doing this for HF was that lots of voltage is developed at the resonant frequency. More than 0.5 volt so it can be rectified very easily and turned into DC to power stufff. This is also easy to do with unused coax and that 50 feet of coax makes a good low frequency antenna. (if you add a capacitor)Experiment a bit, you'll be surprised at how well all different sorts of ad-hoc antennas can work.

author: youta556
author_rank: Contributor
timestamp: May 19, 2022, 10:05:02 pm
content: Is there anyone DIY piezoelectric antenna?reference:https://hackaday.com/2019/04/16/piezoelectric-antennas-for-very-very-low-frequencies/

author: cdev
author_rank: Super Contributor
timestamp: May 20, 2022, 12:35:26 am
content: I would suspect you'd have better luck with electromagnetic focus in an antenna.Maxwell's equations define radio waves and antennas and how they work.I have piezo disks and they almost certainly fail as antennas.It would be a different story if you were trying to use them as microphones which they do very well as.Every little vibration, boy do they pick them up well. On the other hand the high dielectric constant means that many ceramics are very useful for the size reductions they make possible with antennas. They may be subject to phenomena quite similar to piezo effects, but they are not piezoelectric. The biggest and most long distance piezo effect I have ever seen was during the huge earthquake in Eureka California in the 1980s. It was a very large earthquake, and its a miracle more people were not killed or injured. Only one person was, a bank manager who was traveling in his car wityh his family. During the earhquake very bright flashes lit up the early morning sky very brightly. It was thought that these blue-green flashes may have been caused by tremendous piezoelectric charges.. In the surrounding mountains which contained a lot of quartz.. But who knows.. ? Similar flashes have been seen during other earthquakes and are shown on youtube.Okay now I have reada bit more about this ide but not the actual paper yet. Who knows, I am curious what other people here think.This is called a small antenna because of the very large wave length. Because of this, this doesnt seem to fit in to what I know so far. But who knows.. The people at SLAC are physicists who do high voltage stuff for fun.. too.Quote from: youta556 on May 19, 2022, 10:05:02 pm

author: MarkMLl
author_rank: Frequent Contributor
timestamp: May 20, 2022, 07:05:02 am
content: Quote from: cdev on May 20, 2022, 12:35:26 amI think that if it's piezo it's not antenna.I've known people who've worked on things like that in the context of sonar, but it was a long time ago and modern DSP techniques etc. have improved things enormously... Hackaday's featured several projects which make good reading, although the power levels are miniscule compared with the stories I've heard...There are several more useful articles, a good start is using Hackaday's search facility for "phased array". However the one I appreciated most ishttps://hackaday.com/2020/02/15/wall-panels-with-3760-antennas-can-increase-wireless-range/which is useful even without following through to the main paper... I wonder what a minimal ("Arduino-compatible") switching circuit would look like?MarkMLl

author: coppercone2
author_rank: Super Contributor
timestamp: May 20, 2022, 01:44:51 pm
content: https://physicstoday.scitation.org/do/10.1063/pt.6.1.20190530a/full/there is this too, for low frequencies.But it looks like its low power for local communications, because when you need to go for longer range you need a traditional antenna.

author: MarkMLl
author_rank: Frequent Contributor
timestamp: May 20, 2022, 03:27:16 pm
content: Hmm... "Whereas a metal antenna’s equivalent circuit is just a resistor, the equivalent circuit for a piezoelectric antenna is an RLC circuit, and the values for the capacitance and inductance can be tuned using the antenna’s mechanical properties."So I wonder whether that has to literally be an external force, or whether it can be done using a DC signal?MarkMLl

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 20, 2022, 04:11:33 pm
content: To the extent C varies with V (which it usually does for piezo materials), sure.Tim

author: MarkMLl
author_rank: Frequent Contributor
timestamp: May 20, 2022, 06:05:30 pm
content: Quote from: T3sl4co1l on May 20, 2022, 04:11:33 pmDoes C vary with V if the material is unconstrained, or is the whole point that C varies as strain is built up in the material by a V to which it cannot respond by a change of dimension?MarkMLl

author: cdev
author_rank: Super Contributor
timestamp: May 20, 2022, 07:31:40 pm
content: Is this something hams, for example, could experiment with to make better use of the low frequency bands?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 20, 2022, 08:40:01 pm
content: Mechanical bias I don't know. Could be they have equivalent effect.If nothing else, there's a small effect from material strain (somewhat, assuming K is constant under compression I guess), but that's more or less a basic electrostriction effect, much smaller than piezo- or ferro-electric effects.Tim

author: radiolistener
author_rank: Super Contributor
timestamp: May 22, 2022, 01:42:52 am
content: Quote from: youta556 on April 21, 2022, 07:17:22 pm1 kHz full size antenna is about 150 km length. It's too long and almost impossible to build.So, the only way is to use shortened antenna. It needs some radiator and matching device. If you don't expect to transfer high power into this antenna you can try to use magnetic antenna on ferrite rods.Recently I hear about using piezo-crystal as antenna for a low frequency, it uses mechanical resonance effect in the piezo-crystal instead of electric resonance in LC contour as a matching, but it can be complicated for a ham because it requires a special crystal. I have no idea where to find it.