Wideband antenna 50MHz-1GHz - Page 1
Forum section: electronics / rf-microwave

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 25, 2021, 12:34:41 pm
content: I'm looking for a log periodic antenna or other arrangement that can serve to emit in around 0.05 to 1GHz range, for radiated emission testing, low power (4W). Could even use 2-3 antennas if they are cheaper and change them by bands.Any ideas?

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 25, 2021, 02:35:14 pm
content: Maybe this one?https://www.passion-radio.com/wide-band/d150-1038.html

author: ConKbot
author_rank: Super Contributor
timestamp: February 25, 2021, 02:56:41 pm
content: http://www.ets-lindgren.com/products/antennas/biconilogs/4012/401202http://www.ets-lindgren.com/products/antennas/biconilogs/4012/401201How deep is the bosses wallet?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2021, 03:50:52 pm
content: Have even seen multiple antennas used in the lab, the lowest band being a conical dipole or (planar) bowtie type.I've even made this myself (apologies for the terrible photo),just a space frame of wire in a flat bowtie shape, about 1m wide. Works roughly 100MHz+. But just for curiosity's sake, not for real testing. (The balun if you were wondering, is fairly self evident:https://www.seventransistorlabs.com/Images/Bowtie_Balun.jpg)The real trick is calibration. Test labs have the tools to do that. Like, I have no clue what peaks and dips this thing has. If you need the confidence to do precompliance testing, you're probably better off buying a commercial one. (Or go to a lab to calibrate your own construction, but that's probably as expensive, and won't look as nice.)Tim

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 25, 2021, 04:01:17 pm
content: I have a very nice field meter, that I place next to the equipment, like the one some EMC labs do use. Eventually I’m interested in V/m reading. However when it comes to emitting I’m limited to radios and such. So I’m looking something to hook up to my HP rf gen +ampThe discone antenna is very interesting frequency wise, except for being omnidirectional

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2021, 04:03:38 pm
content: Oh so susceptibility as well as emissions?An accurate field meter definitely gets you somewhere!Tim

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 25, 2021, 04:09:49 pm
content: I’m not really interested in emissions, besides all the calibration involved it is not that of a problem in my field , however susceptibility is a harder test, sensitive equipment don’t like rf frequencies. So as long as I can put out as much V/m as possible I’m happy

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 25, 2021, 04:49:22 pm
content: So 5000€ for a log periodical antenna, what are people waiting to start a kickstarter on this instead all the crap that is out there. I would pay 1000€ for such an antenna with not much accuracy nor calibration data etc...https://aaronia.com/antennas/hyperlog-emi-series-directional/

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: February 25, 2021, 08:15:42 pm
content: Sounds like you want a discone.Low, uniform dipole-like gain, flat frequency coverage over a wide range (which sounds ideal for your purpose).Not too hard to build if you have lots of aluminium rod.

author: MartinL
author_rank: Regular Contributor
timestamp: February 26, 2021, 02:55:10 am
content: Tekbox sell a rather tidy little biconical for this sort of purpose, characterised from 30MHz-1GHz (datasheet here:https://www.tekbox.com/product/TBMA1_Manual.pdf):It's only rated for 2W continuous though - are you sure you need 4W in to get the field strengths you want? They do a larger 100W one too but it's only specced for 30-300MHz.

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 26, 2021, 08:09:04 am
content: That seems like a good choice. And if its rated for 2 then 4 will be fine4W is not that much power. For a standard test level of 10V/m you'd need nearly 5W at 1m assuming a gain antenna of 1. For unidirectional antennas it would be lessThere is also this one:https://eleshop.eu/aaronia-bicolog-30100.html

author: MartinL
author_rank: Regular Contributor
timestamp: February 26, 2021, 12:06:12 pm
content: That Aaronia one looks like a better choice in terms of power levels, and the price is similar.My concern with exceeding the power spec is not so much about damage, but that you might saturate something in the balun - meaning the characterisation, which is most of what you're paying for, becomes inaccurate.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 26, 2021, 12:28:57 pm
content: That, or it's really tiny and just burns the hell up.Or also, momentary operation is probably fine (until you're getting saturation -- with attendant distortion -- at the bottom of the band), but keep the duty cycle low, don't hamfist the key...Also, I suppose there could be some equalizing in there (i.e., additional losses in some bands), but probably not much otherwise the efficiency would really suck. Probably just down to winding and core losses.Suppose there could be a tempco in there as well, but again if they're not filtering or equalizing, it's probably pretty negligible.Which, for point of reference, the Minicircuits ZFDC-10-1+ directional coupler has a small pulse transformer inside, around a 5mm cube I think, and is rated for 1-2W. Different ratio, but probably not hugely different power ratings for a balun of similar size. (Wait a minute, it's two transformers isn't it? well, anyway...)Would be easy enough to copy their homework, so to speak, onto a larger core.Give or take calibration, of course; a balun at least should be pretty innocuous, but it is still a matter of how many dB's, over what bandwidth, you want to gamble with.Or, if your calibration requirements are "don't scratch the sticker across the enclosure seam", ignore all that.Tim

author: cdev
author_rank: Super Contributor
timestamp: February 26, 2021, 03:19:22 pm
content: Your best bet is to download an LPDA calculator program, and make one yourself. The resultand LPDA should fit into a perfect triangle of a certain ratio.I have been trying to set up a decent functioning off the air TV setup, which requires a decent broadband highly directional antenna. The choices arent so great but once you get it, they are extremely useful and sometimes they work great. I'd imagine they would be really good for emissions testing because they are very directional.You might also look at the Vivaldi antenna.There are several ways to go about it. I'm working on a planar design to be implemented on both sides of a large piece of cardboard or foam core. using copper tape. PCB material would be too expensive, I gather.I've done this before- Then,the part of the design that seemed the most problematic is the main boom transmission line. It wouldnt hurt if it was a controlled and known impedance. Foam should mhave a dielectric constant of "1" the same as air.Another option is a zig zag antenna implemented in wire, this disposes of the boom. This could also be circularly polarized. Which would be very good for EMC. 50 MHz is going to result in large fragile antennas. Can you trim off some of the low frequency requirement?Quote from: MasterTech on February 25, 2021, 12:34:41 pm

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 26, 2021, 06:02:25 pm
content: Quote from: cdev on February 26, 2021, 03:19:22 pmTests start at 80M, and between that and 300M is the most problematic.

author: cdev
author_rank: Super Contributor
timestamp: February 26, 2021, 06:57:25 pm
content: An HF LPDA is huge, and a commercial one likely costs a small fortune.Quote from: MasterTech on February 26, 2021, 06:02:25 pmYou could likely shrink one a great deal by bending the largest, lowest frequency's elements at a 90 degree angle forward near their ends. By doing that you could maybe shrink the size and reduce its cost by 25% without (much) loss in performanceOr use loading coils.

author: cdev
author_rank: Super Contributor
timestamp: February 26, 2021, 10:54:57 pm
content: Earlier in the thread, OP implied he needed to go down to 3.5 Mhz. I don'yt know if he/she was serious. A magnetic loop or loop stick could do hat, however , but it wouldnt be broadband. A magnetic loop a lain loop with the the ability to tune it in a resonant circuit can be a spectacularly good antenna for its size, however. And the null is very useful.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 26, 2021, 11:35:41 pm
content: Or you drive it untuned -- may take a lot of power, of course! Since it's near field, ehh, it's not as scary as it sounds. Depends on required intensity, as always.And electric field can be done similarly, just field plates around and what have you. Near field tests like these are common in some applications.A TEM cell is kind of the combination of the two, and can be driven matched-impedance for good flatness. About the closest you can come to a pocket-sized (and up) test chamber.Tim

author: cdev
author_rank: Super Contributor
timestamp: February 27, 2021, 01:50:12 am
content: Quote from: T3sl4co1l on February 26, 2021, 11:35:41 pmSort of a box or trap "where the RF goes in but can't get out"?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 27, 2021, 08:54:45 am
content: The TEM cell? Yeah -- idea being, wouldn't it be great if you had a piece of microstrip big enough to put things inside? Controlled impedance and stable geometry, so the fields are well defined, and just stick a terminator at the end so there's no standing waves; inefficient perhaps, but works flat down to DC, hard to complain. Everything's effectively near field inside, at least until you get to frequencies where higher non-TEM00 modes appear, at which point a much more modest sized antenna can take over in free space.I don't know the standards offhand that specify TEM cells, but it's handy for precomp at least.Tim

author: frogg
author_rank: Regular Contributor
timestamp: March 01, 2021, 03:55:12 pm
content: For 4W? Discone for sure. Think CVRJ or JCREW.4W is really not that much power. The biggest danger is to your front-end, but that can be easily mitigated. The antenna itself? Not so much.If you look inside the radomes of RCIED vehicular antenna, it's just a fancy discone. And they use a heckuva lot more power.The following is a list of some publicly available specs. There are a lot more antennas by small USG contractors that cover huge swaths of bandwidth for vehicular EW.https://www.antennaexperts.in/product-detail.asp?cat=jammer-antenna&id=31

author: PartialDischarge
author_rank: Super Contributor
timestamp: March 01, 2021, 06:29:20 pm
content: For the price the discones seem a nice choice. The lack of unidirectional gain can be actually offset by using a larger RF amp, which is going to be cheaper than a logper antenna, weird.

author: cdev
author_rank: Super Contributor
timestamp: March 04, 2021, 06:41:14 pm
content: Did you try putting a reflector behind it?I am thinking about building this and using it for local broadcast TV. The balun is the most interesting aspect of it to me. Did you have an inspiration for this balun?I like antennas I can hang from a hook on the ceiling and turn from my desk. I have some copper HVAC tubing which would be ideal to construct it out of.Quote from: T3sl4co1l on February 25, 2021, 03:50:52 pm

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 04, 2021, 07:53:55 pm
content: No, but I imagine that would be fine. Follow any other reflector-bowtie design guide for ideas.I think the effect would be, at least particularly at high frequencies (wavelength much shorter than the total element length), you should get exaggerated axial side lobes, as the reflector acts as a ground plane with respect to an individual element; the same element also acts to shadow the element behind it, so the waves don't cancel out as well as they would for a resonant (thin) dipole. In addition, you have the horn mode between elements, which, how... ahem... "horny" that acts, depends on the angle between them. If you mean to keep everything parallel, that'll do weird things for frequency response (standing waves between elements and reflector), while if the elements are inclined (with the vertex touching reflector, as a ground plane), you get some sort of TEM horn mode for each element to the reflector, and to each other. And probably, those lobes split up into sub-lobes as you go up in frequency, as they tend to do.So, if it's for a single frequency, probably it doesn't matter much what shape the dipole is, as long as it's a half wave in front of the reflector; else if wideband, a different symmetry should probably be considered.In any case, easy enough to plug into a simulator (for certain values of "easy"..).If you want more directionality, you may find a horn proper, or log periodic (including the zig-zag or spiral element patterns on the same skeleton), to be more effective?The balun, is simply two 100Ω twisted-pair transmission lines, wired in parallel to the 50Ω port, and wired in series to the feedpoint, thus getting 200Ω differential (the center tap is grounded). Ferrite beads allow them to be wired arbitrarily, thus making a transmission line transformer, with a cutoff probably in the 10s MHz, depending on how much loss you want to accept, as those ferrite beads are pretty good resistors in that range.I don't know exactly what impedance the antenna is, but return loss is on the order of 10dB above 160MHz, and I don't really have a good signal source to tell beyond 400MHz, it might be worse up there, or it's just down in the noise floor (alas, I'm still slumming it without a VNA). So, not a terrifying mismatch. I do see ambient signals up to 900MHz, probably beyond that but my spec's noise floor is just too high. I assume the actual passband is a bit of a forest up there, given the somewhat haphazard arrangement of wires. A sheet bowtie, or proper cone, should be flatter, of course.Tim

author: cdev
author_rank: Super Contributor
timestamp: March 06, 2021, 03:29:14 am
content: Thank you! Your bowtie balun + antenna seems like it may be quite similar electrically to a knockoff I made of the switchable elecraft balun It also has the ground plane behind it and has two approximately 100 ohm transmission lines wired in parallel which can be configured in series (for 4:1 mode or in parallel). That kind of configuration is very broadband. I used two big binocular "cubeular" binocular cores for it. It does work all the way up to 6m. And it can be used for VHF digital TV. and receiving FM BCB and two meter dx.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 12, 2021, 03:32:04 pm
content: Like many radio amateurs, I would like to try measuring near field EMF levels. It is said to be difficult compared to using charts, or spreadsheets.I have a calibrated hand held spectrum analyser, but lack an e-field antenna. Using a 6 inch antenna to obtain some idea of the levels involved in the near field of a 3.5 MHz dipole with 10 Watts, it produced easy to measure levels in dBm.However, how do you equate Volts per metre to the length of a short dipole?

author: LaserSteve
author_rank: Super Contributor
timestamp: March 12, 2021, 06:59:09 pm
content: Try WA5VBJ's1 log periodic PCB antennas for 300 and up. You said broadband, you did not say FLAT... Some of his receive well outside their range, like the big log periodic.here is one of his efforts for ultra broadband.https://www.wa5vjb.com/references/PlanarDiskAntennas.pdfSteve

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 12, 2021, 07:09:20 pm
content: These antennas are for 100 MHz and higher, I am looking to work out how to calibrate a small dipole for use on lower HF frequencies.But thanks

author: cdev
author_rank: Super Contributor
timestamp: March 12, 2021, 08:42:27 pm
content: Maybe a loop antenna would be best for you.A HF dipole could be huge.Lower HF antennas are large enough to make rotating them difficult at best. Would you want a helicopter parked in your back yard, with its rotating blades. A dipole might approximate that.Calibration? I would expect them to vary significantly with orientation and height.For a stationary antenna, and a single, fixed direction, You might be able to extract the parameters with a VNA, at a fixed interval, say 1 MHz, and then use a spreadsheet to apply a correction factor "mask"-like over the raw DUT measurements to get the corrected response.I suspect that would only work if the impedance was constant and known, which is unlikely, though.Quote from: Solder_Junkie on March 12, 2021, 07:09:20 pmThe dipole likely will have a smoother response if you use the special balun which they use of biconical EMC antennas.I don't know if you can approximate a biconical antenna with what you have, but I have attempted to build a great many broadband antennas in a repeatable manner, and I can assure you that the response of a vertically polarized bowtie or biconical or planar disk antenna (the last one, mentioned by Laser Steve above, is a particularly easy and useful antenna, and very easy to construct, using two conducting circular disks, like pizza pans, and a stick. It eliminates the need for a balun if you properlyground he shield to the bottom, but it is finicky. You have to do it completely.You could try a horizotal "bowtie on a stick" like that of T3sl4co1l Tim, above. - that bowtie shape I think could give you a more manageable antenna for any given frequency, size wise. Shortening its wingspan by at least 25%With his or another balun, (i'm attachinga design below, this might work well, set to the 1:1 setting. It is likely to be much more broadband than any dipole you'll ever be able to make. Try it. Its a good start. Youre unlikely to find a way to fit more "antenna usefulness" into the space. isnt that usually the challenge?Its not impossible to get an antenna that works over a 10:1 frequency ratio. 100-1000 MHz is not that difficult. And the construction is much easier than a discone. Make sure to use a balun,if you feed it with coax you'll have to.Amplified active broadband e-field antenna.As far as an e-field antenna, there you can utilize something like a mini-whip high impedance amplified antenna.https://circuitsalad.com/2020/02/13/simple-low-current-mini-whip-antenna/it will give you a good VLF antenna in a small space and may perform surprisingly well if you get it far enough away from your house and its noise field. It works on capacitance.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 12, 2021, 09:29:30 pm
content: Sorry, I missed a zero when I read your post. Old Eyes do that.NIST / NBS is your friend on calibration publications for antennas. Here attached is an example for a vertical monopole and a horizontal dipole. . If you keep digging you'll find publications for other designs / frequency ranges as well as Reference antenna designs with known gain.Generally you can contact NIST's specialists with a little legwork and get your questions answered with a phone call or email if you are patient and persistant. Other standards agencies will also have publications out.They do have an antenna lab at NIST.Keywords I used: NBS antenna calibration NIST antenna calibration. NBS STANDARD DIPOLE NIST Standard Dipole and so forth...You find things like this as well...https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote1098.pdfMost of this work would have been done back in the day when they were still "National Bureau of Standards".Ultra-broadband amplifiers come from Amplifier Research, and mine covers 10 Khz to 1 Ghz at 50 Watts. Their "Orange Book" is quite a good read. If you do some digging over time usually you can find an AR amplifier on Ebay for a fraction of the 3000$ going rate.Steve

author: cdev
author_rank: Super Contributor
timestamp: March 13, 2021, 12:12:47 am
content: Quote from: T3sl4co1l on February 25, 2021, 03:50:52 pm

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 13, 2021, 07:49:30 am
content: Thanks Steve and TimThose NIST publications are really useful. I have a couple of home made active antennas, but my preference is for an electrically very short dipole of around 1/100th the size of a half wave one. On my hand held spectrum analyser the near field levels from 10 Watts fed into a half wave (full size) dipole on 3.5 MHz are around -50dBm to -20dBm.The idea of the very small test dipole is (a) the levels are well within the range of the SA and are safe to measure, (b) the levels vary smoothly as I walk around the area of the transmitting antenna and (c) being electrically very short there shouldn’t be any unexpected “dips and troughs” in the response due to resonance, etc. The problem is one of calibration of the antenna factor...

author: LaserSteve
author_rank: Super Contributor
timestamp: March 13, 2021, 04:42:17 pm
content: The NBS pub on UHF had something similar the excessively short dipole of which you speak. I'm away from the work computer where I have Googles AItrained to give me precisely what I want, well, as much as possible, but I'll try to find it.Update, Try NBS technical note 1098.The only reason I know about the NBS notes was a former employer wanted a field strength of X permeter over a buried wire for a test. Somebody asked him to have me play as Team B for a sanity check.Otherwise this is not my field of interest, which is RF driven acousto-optics Rf excited gas lasers,, and UHF/Microwave Ham.Steve