Paper on teflon absorbing properties, your opinion - Page 1
Forum section: electronics / rf-microwave

author: yl3akb
author_rank: Regular Contributor
timestamp: July 03, 2025, 04:17:24 am
content: Hi all! Came across this 'scientific' paper:https://www.researchgate.net/publication/349750550_Microwave_absorbing_properties_of_teflon_coating_for_x-band_frequenciesThey claim that teflon acts as microwave absorber at ~10GHz (and others) based on return loss measurement of sample put inside waveguide. In my opinion that's nonsense, because, of course the RL will be all over the place due to impedance mismatch created by dielectric sheet, absorbing or not.What's your opinion? Am I missing something?

author: abeyer
author_rank: Frequent Contributor
timestamp: July 03, 2025, 05:45:48 am
content: Like this?https://en.wikipedia.org/wiki/Nicolson%E2%80%93Ross%E2%80%93Weir_method

author: Hamelec
author_rank: Regular Contributor
timestamp: July 03, 2025, 06:06:29 pm
content: Quote from: yl3akb on July 03, 2025, 04:17:24 amIMHO: nonsens

author: joeqsmith
author_rank: Super Contributor
timestamp: July 03, 2025, 07:35:21 pm
content: Quote from: yl3akb on July 03, 2025, 04:17:24 amOpinion? Isn't it easy enough to stuff some Teflon into a calibrated setup see if it makes any difference? Figure 4, showing RL for thicknesses up to 8mm. I would assume even thicker would be easy to detect.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 03, 2025, 08:57:21 pm
content: Cut out a section of 6.43mm thick Teflon to fit inside the WR90. Used the LiteVNA64 with homemade frequency extender and homemade short and offsets. Narda load and sliding mismatch load were also used.I did not bolt or clamp together the parts. Rather just stack them up and aligned with fingers and called it good enough. First test swept from 8.8 to 9.2GHz. From their paper I would expect about a 4-5dB RL.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 03, 2025, 09:12:16 pm
content: At 10GHz, I would expect a RL approaching 12dB. VNA was calibrated from 9.8 to 10.2GHz. Again, nothing was clamped and parts were hand aligned. Its just to get some idea if it behaves as paper suggests. I did compare the VSWR (for the hams) using the load and sliding load. The Narda mismatch standard has a VSWR of 1.353. The Narda load 1.015 max. Seems close enough...Rather than the published 12dB, I measure less than 1dB. It could be my homemade frequency extender. Someone once suggested my math for the waveguide was incorrect. My homemade standards are based on the Agilent X11644A. There could also be problems there. Maybe my Teflon is not 100% pure.All I can offer is that my quick test failed to yield anything close to the suggested RL provided in the paper.

author: coppercone2
author_rank: Super Contributor
timestamp: July 03, 2025, 10:31:49 pm
content: Dielectric filled waveguide is a thing and its well documented and can be anything from a gas to a liquid to solid plasticyou would start herehttps://www.microwaves101.com/encyclopedias/dielectric-loaded-waveguideI believe I even heard of ultra pure water filled waveguides, that have a little circulator pump connected to keep the water cold and filteredthe most interesting one is the microwave plasma welder, which is essentially a dielectric filled waveguide with a outlet . some where there is a big book about it. It gets you oxy-gas torch performance from a electronic system

author: joeqsmith
author_rank: Super Contributor
timestamp: July 04, 2025, 12:54:02 am
content: I guess all waveguides are filled with something.Time to break out the vacuum grease, rough and TMP then prove me wrong!

author: ejeffrey
author_rank: Super Contributor
timestamp: July 04, 2025, 03:28:10 am
content: The method of using a dielectric filled waveguide and VNA for measuring dielectric properties is totally sound. But their results make no sense to me, or I am totally misunderstanding their claim. PTFE is widely used as the dielectric spacer in high frequency coaxial cables. It has acceptably loss for that application, it's not a strong microwave absorber by itself. "Teflon" is a trade name that comes in different formulations but I don't see any indication that they are using a something special. Am I missing something?

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2025, 04:25:46 am
content: well when they design a cable dimensions of everything are taken into accountif you just whack some thing meant to be filled with air it will change some of the properties ....its going to look like a discontinuity unless its designed for that fillerBut have a look at loss. You will find air coaxial pipe has the lowest loss. Like db/distanceI think it has to do with thishttps://en.wikipedia.org/wiki/Dielectric_heatingAn alternating electric field will polarize and rotate the polarization of a material. Much like induction heating for magnets.https://www.scielo.br/j/bjp/a/Gh5ndHdgvpxfQcFZTycX3Xh/?lang=en&format=pdfAlso interesting in a offhand kind of wayhttps://en.wikipedia.org/wiki/Thermo-dielectric_effectit helps to understand all the behaviors of the materials you are asking about (non conductors)Perhaps it has something to do with reaching some critical level for the field strength? It might not be linear.The idea with dielectric waveguide fills I think has mainly to do with making it harder for it to arc. But it increases losses, so it might actually need cooling.I think it mainly has to do with the idea that you can visualize for a moment in time a electric field in some location of the waveguide (the E and H fields). If the electric field is there, its having a effect on the dielectric material in that location, even if for a short time... just as if it was a standard capacitor componentI think they were working on dielectric heater ovens instead of MW ovens too, but it was way too expensive and they don't even know if the food would taste good. I always noticed I feel better about my food if I heat it in a regular oven......Also, VNA "power" measurements are of course a whole new dimension that is not often studied by most people. Who actually tried to put a 10W amplifier on their VNA? They say it can get very non linear.The behavior of dielectrics really screws people up when they try to get into HV design. it seems like a whole new world to me, but its rather messy to play with that stuff. Usually for normal electronics you can almost completely ignore it, save for sample and hold circuits.

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2025, 04:55:20 am
content: Also I am not that familiar with cabling for high frequencies.All the cables I use have a PTFE tape in them. Like plumbers tape. This is kind of a compromise between foam and solid. I think % wise, it has alot of air in there.Do they havesolidPTFE core 13GHz coaxial cable?The common cables start to have rather high losses at frequencies higher then a handful of GHz.If you can find the transmission plot for a solid PTFE core cable at that frequency range it might help with reasoning if those loss figures are accurateData of dielectric constant vs frequency (or magnetic behavior vs frequency) proved illusive to find for me. I looked for that data before. I was hoping of a CRC handbook, but there is a giant amount of missing info.I think that the basis of this experiment is " rectangular dielectric waveguide (RDWG) technique "Here appears to be a similar experimenthttps://eprints.whiterose.ac.uk/id/eprint/722/1/pollardrd1.pdfBut it looks like its conventionally measured in free space with antennas, rather then inside of a wave guide.What is the benefit of trying to measure it as a waveguide insert rather then in free space?Because if I would do it, it would be like the experiment I linked with the antennas, rather then making a custom insert.The only thing that comes to mind is that the field intensity is higher if its in a insert (with respect to the size)

author: yl3akb
author_rank: Regular Contributor
timestamp: July 04, 2025, 05:42:54 am
content: Quote from: joeqsmith on July 03, 2025, 08:57:21 pmThank you for the test! But how did your waveguide-dielectric setup actually looked? From your pictures I conclude that your setup had a gap (filled with PTFE) between the metallic flanges, and that would explain why you measured <0dB RL dip in case of teflon+short, but thats due to radiation from the gap, not absorption in dielectric.I would expect that PTFE insert completely surrounded by metallic waveguide terminated with short would still measure RL=0dB (okay very slightly below, because of course there is some loss in PTFE, but numbers would be far from the absorber characteristic).

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2025, 06:54:20 am
content: if it was actually 0.12dB then it would make sense. A decimal point?\But here is another... discredit to this method... they sell special objects to put in the chassis to get rid of reduce resonance inside of a assembly from 5-10 GHz or so. Like glue on ferrite tiles. You would think if teflon would be any good they would sell plastic ones... its a rather expensive component . You are supposed to put them on the lid of a enclosure over the PCB.BTW I think the test setup in this thread is probably very fine for something that is supposed to do 12dB of loss. I noticed that these experiments are not THAT sensitive. I loosened some waveguide up and was fooling around with it.. and it seems pretty tollerant.But is that not surprising that there is so many people involved in making such a controversial claim with really good R&S equipment??

author: ftg
author_rank: Frequent Contributor
timestamp: July 04, 2025, 07:06:32 am
content: Quote from: joeqsmith on July 03, 2025, 07:35:21 pmThe only sample the actually seem to measure is the "22.8 mm×10.1 mm×4.0 mm (±0.05)" one.They calculate the values for all other thicknesses in the charts from the parameters they derive from that initial measurement.So out of "1, 2, 3, 4, 5, 6, 7, and 8 mm", only 4mm was measured, others are derived from that measurement.

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2025, 07:22:53 am
content: PTFEish low frequencyPTFE high frequency (for a lens, but of same material and similar thickness/size of their sample)https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1627I think this thread would be helped by someone finding a good graph for PTFE loss vs frequency that covers the frequency of interestIs it not possible to calculate the loss tangent from their experiment and see if it matches up to some graph related to PTFE? To an accuracy of an order of magnitude.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 04, 2025, 09:22:12 am
content: Quote from: coppercone2 on July 04, 2025, 07:22:53 amExactly, the PTFE is one of the lowest-loss dense dielectrics available, its just surprises me, that professional researchers would try to prove and call PTFE RF absorbing material (90% absorption!!) and such paper would slip trough?

author: yl3akb
author_rank: Regular Contributor
timestamp: July 04, 2025, 09:26:26 am
content: Quote from: coppercone2 on July 04, 2025, 06:54:20 amits definitely not a typo

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2025, 09:35:36 am
content: Well the main problem for me is that1) no one provided a (external) graph of loss of ptfe across the relevant frequency range2) no one did the calculation to see what the loss is in that object with the assumed lossIDK how you can say for sure unless you have a coefficient and a ballpark equationI don't follow the math in the paper. To me it should be1) example calculation2) attempt at solving the problem mathematically with #13) measurementthe paper is all over the place.Introduction -> resultsIts missingintroduction -> theory (math solving) -> resultsLike finding a reputable source of information to see if the little low res graph they have for the material coefficents for teflon they use for their equation is accurateand the other huge problem is like a lack of a control. They should run the same experiment empty without anything in the same holder and show both curves. Any apparatus without a 'control' for sanity testing is severely flawed. It can't rely on the equipment cal, there has to be like a physical thing with that setup to prove it. There has to be like a experiment that shows a expected result from their test fixture. While you are using it to determine an unknown it should have a known result of some kind that validates it. I would reject that paper on first review for lack of a setup verification. We always do it (i.e. short meter probes to check if leads are connected)...............i think the lack of a 'control' result is qualification for instant rejection, especially when the claims are wild. It's like a bullshitter calling card IMOBut what I was getting at is maybe someone here knows how to calculate the theoretical loss from teflon of that size with coefficents that are trusted to see what is expected . Like someone that knows how to use waveguide sim softwareand I am not certain but I think it can be some how defined like "the empty wave guide has a impedance of x, and the teflon filled section has impedance y".. so it turns into a circuit that can be analyzedbut lol I am thinking to set up a little loop of wave guide on the VNA and then stuff teflon pieces in there. If their right it should be lossy. I have a big sheet of teflon but I would need to cut that up so it can fit. But I also feel dumb because I have a feeling its a AI that is conning me into assembling waveguide for no reason. I think someone here has already jumped on that grenade

author: joeqsmith
author_rank: Super Contributor
timestamp: July 04, 2025, 02:48:01 pm
content: Quote from: yl3akb on July 04, 2025, 05:42:54 amMeasured transition with a short then placed the Teflon into the transition and reattached the short. I don't know what gap you would be referring to. If you wanted to sketch up a drawing of how you would like to see it configured, I could repeat the test easy enough.

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2025, 07:11:34 pm
content: What I wonder is what it would take to get 12dB. Like how much carbon powder in elemers glue

author: yl3akb
author_rank: Regular Contributor
timestamp: July 05, 2025, 05:33:53 am
content: Quote from: joeqsmith on July 04, 2025, 02:48:01 pmWhat confuses me is why is there a 2..3 dB dip at ~9 GHz in case of short+PTFE, it should not be there. My only explanation would be there are radiation losses somewhere.And your test pieces look, like they create the gap, that would radiate (see attached).

author: coppercone2
author_rank: Super Contributor
timestamp: July 05, 2025, 05:51:20 am
content: i thought he is just showing how he makes it to know where the edge isthe easy way to make a block is to make it with a flange so it can be easy to fasten to the machine and then keep trimming it until its a good fit then just cut it flushyou can get alot of error in machining if you keep taking it off the machine to rotate it and stuff in jaws, and there is always a question if its trueso if you cut it out of a flat sheet fastened to machine it is as perfect as the machine alignmentand its extra harder on soft slippery teflon that will shoot out of a vise like a banana peel, also, its the only way to fasten it without squishing it and changing it dimensionally. this is a reason you always get people way more material then the part actually needs. You would probobly cut it down very thin, break it out and then sand the ripped part offand you need to use all the tricks because its not easy to like attach it to grinders to flatten it and whatnot, unless you have some special expensive equipment... I see with alot of plastic sheet materails they start warping pretty bad. I heard you basically can't make some more complicated parts from teflon if the stock is 'bad'... its almost like welding engineering design then (where you need to figure out how to deal with the warp)

author: joeqsmith
author_rank: Super Contributor
timestamp: July 05, 2025, 02:39:08 pm
content: Quote from: yl3akb on July 05, 2025, 05:33:53 amOh, now I see the first problem. The white shown in those photos are covers used to protect the ends of the waveguides. These are not part of the measurement. As far as sealing the waveguide (or having a gap), now that I understand what you are referring to... As I mentioned, I did not bolt the waveguides together nor did I make any real attempt to align them for this test. Still you can from the mismatch load, the values read were in reasonable once calibrated.I ran a similar test about a year ago where I inserted a quartz test tube into a waveguide. In this case we are looking at S21 with a bridge circuit (magic Tee).https://youtu.be/ujQge2k6B6Y?list=PLZSS2ajxhiQCyzRPSGkWSWfboP-5MfqWF

author: joeqsmith
author_rank: Super Contributor
timestamp: July 05, 2025, 02:50:40 pm
content: Quote from: coppercone2 on July 05, 2025, 05:51:20 amSorry to disappoint you but my tool of choice was an X-acto knife. Teflon is easy to cut. Early on I ran a similar test looking at S21 without the frequency extender using WR102. I looked at Teflon, some sort of rubber, and LEXAN.https://youtu.be/xe4Fy4Lpnqw?list=PLZSS2ajxhiQCyzRPSGkWSWfboP-5MfqWF&t=2866

author: coppercone2
author_rank: Super Contributor
timestamp: July 05, 2025, 05:19:44 pm
content: did not come to mind, I heard enough stories to stop using exacto on thick objectsmy least favorite tool, one groggy moment and you are in the er

author: yl3akb
author_rank: Regular Contributor
timestamp: July 05, 2025, 05:49:34 pm
content: Quote from: joeqsmith on July 05, 2025, 02:39:08 pmThen your setup looks okay - yes, I confused those covers for teflon test pieces, never mind...

author: joeqsmith
author_rank: Super Contributor
timestamp: July 05, 2025, 07:16:03 pm
content: If you watched that last you could see even with Teflon at these lower frequencies, there was some loss. You could also see that I ran a repeatability test, swapping the parts in/out and reassembling the setup (again, no bolts or real attempt to align it). You could also see about a 4dB loss around 6.6GHz.Now why my results vary so much compared with the paper you linked, I can't say. There are a lot of variables. I have used this same setup to make several measurements and results always seem reasonable, but we are comparing a $150 VNA + say $1000 of additional hardware, homemade standard and home written software against their Rohde Schwarz ZVA 67.Maybe @pdenisowski @virtualparticles @Joel_Dunsmore who would all have access to higher end equipment could comment or better, repeat the test. I have that old Agilent but am limited to 9GHz.Quote

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 03:12:28 am
content: Repeating the test shown in that video, measuring S21 at 10GHz with the homemade frequency converter and WR90. The two transitions are part of a university microwave training kit. They are not very good. The two were butted up to one another and a baseline was stored to normalize the data to 0dB. I then inserted the shorting plate between the two to show the dynamic range (about 55dB). Next, the 6.43mm thick Teflon block was placed between the two transitions and I measured 5dB of insertion loss. As a sanity check, a Maury Microwave fixed 10dB attenuator was inserted. The attenuator is specified from 8.5 to 9.6GHz.Again, nothing was bolted together and I was aligning the parts with my fingers. The Teflon measures similar to the insertion losses seen during the previous tests at lower frequencies.QuoteMy opinion based on these tests is that Teflon does indeed absorb RF in the X-band. But again, feel free to reproduce the tests yourselves and show your own data.

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 04:08:09 am
content: I guess their not kidding when they say you can't just whack any old plastic into a radome and there is actually engineering involvedand it could explain those potted WIFI antenna problems people write about

author: yl3akb
author_rank: Regular Contributor
timestamp: July 06, 2025, 05:57:05 am
content: Quote from: joeqsmith on July 06, 2025, 03:12:28 amSomething is still wrong, those 5 dB cant be due to absorption. I did quick EM simulation using your dimensions (WR90 and 6.43mm teflon) and lossy PTFE model and I get S21 ~ -1.1 dB, but thats purely due to reflection (S11 is poor -6 dB, due to huge mismatch caused by different dielectric constant section). Why you measure -5 dB, I dont know... Could it be that your measurement setup cant deal with reflective DUTs?

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 06:15:25 am
content: The through measurement should be S21the reflected measurement should be S11And your simulation says the S11 will be almost all of the signal missing from S21.Even if the value is wrong, seeing the difference between S21 and S11 would determine if its dissipation or just causing a mismatch. Measuring it with a directional coupler would still resolve the issue IMO, because who cares about magnitude, if you can prove its just reflecting it, it means the paper is bullshitMy unknowlegable first opinion was that a teflon filled waveguide is the rough equivalent to basically changing the wave guide size. So if the setup is WR75, the teflon piece is something like a segment of WR90 that got spliced into the circuit.But none the less this leads to another interesting thought, what would happen if the teflon part was not just a block, but a taper shape. Because if the teflon is a block, its an abrupt impedance change, because suddenly there is a wall of dielectric changing the wave guide. But what if you had a extended hexagon shape in there, so the dielectric appears in the middle, and gradually occupies the full space of the waveguide, like this drawing. Then its kind of like a virtual taper?While you got that simulation open, can you tell me what that does?Because when I took apart this old attenuator, it had a 'arrow' shape like that for the silver ceramic rotary 'attenuator'. It was sharp on one end (very much like a machinists thread 'fish gage'). I wonder if the purpose of that is to reduce reflectionOr the inverse of that shape might work better, i.e. to put a bowtie pasta teflon shape into the waveguide.Actually maybe the attenuator was a bowtie shape. I don't remember.yeah OK i got it, they are called resistive cardswhat if you make one out of teflon that occupies the entire waveguide interior , so its not just a abrupt plug

author: yl3akb
author_rank: Regular Contributor
timestamp: July 06, 2025, 06:47:09 am
content: Quote from: coppercone2 on July 06, 2025, 06:15:25 am\Of course, it does the expected and without reflection S21 becomes close to zero. Here is simulation with 20mm tapers added at both sides.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 06, 2025, 06:50:02 am
content: Quote from: coppercone2 on July 06, 2025, 06:15:25 amNo point to do the simulation - it will be perfectly matched and only loss would be due to very small dissipation factor (loss tangent) of PTFE (you posted the graphs while ago)

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 06:53:11 am
content: Ok, if you really wanted to prove it without having a directional coupler, you can build that and get true results, if you get the geometry correct, to measure if its lossy with only a through.Anyway,. so now it just depends on if the simulator is wrong. I still appreciate the effort to check the simulator, you never really know.I wonder if the whole paper is a typo because of someone looking at the wrong plot

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 06:58:48 am
content: Actually I did read it carefully, they do say "reflection loss". Its not dissipation.So maybe they just think because it causes a reflection in a wave guide it would cause a reflection in free space?But the way its written all points to.... it being a conventional absorber.I wonder if the dean of EE at university of Jakarta cares

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 10:29:48 am
content: Quote from: yl3akb on July 06, 2025, 05:57:05 amI have updated my previous graphs to include additional text as apparently it was not clear. When looking at the return loss, I show two different Narda standards. One was the load used to calibrate the VNA, the other a reflective load. The reflective load (or mismatch load) has a VSWR of 1.353 or return loss of 16.48dB. I showed the data in VSWR for the hams but no matter. That sanity check seems correct showing that the setup can indeed measure a reflective load.With my setup, the Teflon measures about a 1dB return loss (S11) and a 5-6dB insertion loss (S21).

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 03:27:23 pm
content: Quote from: yl3akb on July 04, 2025, 05:42:54 amWhat is interesting is your first comment about S11 with the Teflon and closed off waveguide having a 0dB return loss is basically what I measure at 10GHz.Quote from: joeqsmith on July 06, 2025, 10:29:48 amBut when you run the simulation, S11 is very close to what I measure for S21. Your S21 is very close to what I measure for S11.Quote from: yl3akb on July 06, 2025, 05:57:05 amIt's almost like these two simulations are swapped. Really strange.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 04:25:05 pm
content: I remeasured S11 and saved the Touchstone data so I could place it all onto one graph. Again showing the standard shorting plate, Narda mismatch load standard (16.5dB), Narda load used to cal the VNA, and the Teflon sample + the shorting plate.I have also included the Touchstone files for these measurements.You could provide the model for your setup (assuming someone else has access to the EM simulation tools you are using) maybe we could figure out why there is such a discrepancy between my measurements and your simulation.

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 05:01:39 pm
content: this document by a ptfe manufacturer cites teflons dissipation @ 10GHz in a specific non graph single point measurement as very low, but keep in mind it likely has a 10-20% glass filllhttps://www.craneae.com/sites/default/files/documents/taking-advantage-pure-ptfe-qualities-microwave-substrates_0.pdfDissipation factor is0.0013I wonder if bogus teflon manufacturers are adding something to the teflon to make it easier or cheaper to make. I heard most cheap plastics are.... adultrated with random shitAnother big red flag from the paper is... indonesian materials market, which means they used a aliexpress knockoff to source the sample.Where did you get the teflon for your experiment? I know the sheet I Have is very expensive (cost $1000 or more), because someone bought it from MMC. The reason I have it is because it warped to feature more then a 10 degree bend from being stored on its side between cabinets filled with test leads, so it sagged. Apparently it should be stored laying flat on a flat surface not on edgeI wonder if a electrometer could be used to test it. Conductivity should be effected by additives.. but that is not a easy measurement to do either. Something like two copper patches put over ptfe and weighed down to measure the resistance between them, or using the weights from a ESD mat tester (which actually uses conductive rubber for a electrode, under a weight, because its a short circuit compared to the very high resistance it measures). But the meter itself is not suitable because its logarithmic, you would need a test equipment. Fortunately I no longer have a electrometer to cause me bother

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 06:42:09 pm
content: Quote from: coppercone2 on July 06, 2025, 05:01:39 pmThat scrap must be at least 30 years old now. I just hack off a bit when needed. Most likely came from McMaster-Carr as that's my go to. Most likely this part:https://www.mcmaster.com/8545K1/Fairly inexpensive if someone wanted to try and replicate my results using a higher end setup.

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 06:49:00 pm
content: kinda exciting if the simulator is wrongWhat is the theoretical reason for this. If the D factor is low, and the reflection reading is different. Magnitude I can understand there being a discrepancy because of equipment... but the ratio of absorbed to reflected should be similar IMO. I don't see why your equipment would be wrong if it reads the standard correctly... that is two points.Only easy thing would be to test to see if a 5db attenuator attenuates 5db.. to test it @ that specific level. My LNA had a problem where it had a deep null around.... 700MHz IIRC. after it got damaged some how. When I characterized it, it looked like a notch filter. But that kind of thing should be detected by even 1 cal sweep for 1 standard.Can you connect a variable attenuator to that test setup it in series and sweep the range to see if its linear enough in regards to adjusting the attenuator? I don't think it would matter where it is or what kind (coaxial or waveguide), or just thread on a 5db attenuator .Then there is always the option if available to measure reflection @ fixed frequency with a RF power meter to see if it agrees with your sweep, since it easily plugs into the output or reflection port.I think the power meter would be king at finding problems that are thought to be equipment related

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 07:29:28 pm
content: While I did measure a Maury Microwave fixed 10dB attenuator and saw reasonable results, I don't have a lot of what I would consider high quality parts. I bought what I needed to run that electron spin experiment, along with those couple of decent loads and one stepped short for calibration/verification. Most of what I have are from a university training kit. These parts are really just to expose the students to waveguides. The variable attenuators are not anything I would hang my hat on.My coaxial step attenuators are all low frequency (2-4GHz ish). I have ran tests using fixed attenuators which is documented in the user's manual.

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 07:33:26 pm
content: that looks pretty accurate. IDK then lol.

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 07:45:57 pm
content: Since its easy to cut with a knife by scoring, how about trying a piece of acrylic in the same setup?Oh I know, a piece of styrofoam

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 07:46:16 pm
content: Basically, I have two of these kits in loose form with both tube and solid state sources. An erector set for RF noobs like myself. Lots of fun, low investment and a great way to get an introduction.https://www.manualslib.com/manual/1610253/Lrl-550b-Ss.htmlhttps://www.ebay.com/itm/187172557899

author: joeqsmith
author_rank: Super Contributor
timestamp: July 06, 2025, 07:49:28 pm
content: Quote from: coppercone2 on July 06, 2025, 07:45:57 pmI don't think running random samples adds anything to the conversation.

author: coppercone2
author_rank: Super Contributor
timestamp: July 06, 2025, 07:56:17 pm
content: I did random material samples (solid conductors made by machine shop) for a test fixture and it did turn up some interesting results at work for a different kind of electrical test, enough to get someone to redesign the test because of unexplained results. No one could answer why , but it was not investigated, they just went to another method, because the fixture/test idea was clearly not bomb proof. But that experiment is not for EEVBLOG. That particular material was not relevant but the theory regarding that type of material was thought to be completely obvious but the test results were weird. It was very interesting to see, since the experiment feels like something you would have done in a 1950's university class.People always seem to say the old text books focused on very 'simple' stuff that can all be distilled to 1/2 page now. Not so sure anymore.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 06, 2025, 11:40:45 pm
content: Quote from: joeqsmith on July 04, 2025, 12:54:02 amUsually pressurised with dried air or nitrogen, but that is to try to prevent the ingress of moisture.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 07, 2025, 05:59:15 am
content: Quote from: joeqsmith on July 06, 2025, 03:27:23 pmhmm, the first comment about RL=0dB was about teflon+short (single port measurement), and in your future post graph I see that you got near 0 dB so it looks good.But simulation was for two port case. If by 'swapped' you mean swapped S11 and S21 results, the I agree - I got S21 = 1dB, S11 = 6 dB, but you got S21 = 6 dB, S11 = 1 dB. Could there be a chance that you have somehow swapped channels in your software ?In any case the math in case of both combination work out in favor of theory that measured loss is due to reflection not absorption. In your case it measures more reflective, so that's why you got more transfer loss. What's the reason for this discrepancy with simulation, I don't know, but its definitely not an random error.

author: ConKbot
author_rank: Super Contributor
timestamp: July 07, 2025, 12:49:53 pm
content: A lot of RF papers are hot garbage. "I simulated a 2.4 ghz antenna, built it and it came out at 3.8 GHz, ok here are plots" with no refinement of the model find the difference from the real thing. "we made a circular polarized antenna, ok here is a plot of return loss vs parameter were sweeping" with no polarization measurements. So you have to keep your wits about you. Stuff like this where mismatch is causing a reflection, not actual loss, and the paper being a little unclear about it seems to be par for the course.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 07, 2025, 12:51:39 pm
content: Quote from: vk6zgo on July 06, 2025, 11:40:45 pmI tend to agree as air is made up of about 78% nitrogen and atmospheric pressure is about 14.7 psi.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 07, 2025, 12:54:55 pm
content: Quote from: yl3akb on July 07, 2025, 05:59:15 amI measured and provided data for two different known parts. One for S11, the other for S21. Both measured as expected. I guess you could cap off one end of your waveguide simulation and see if you measure about a dB RL.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 07, 2025, 01:34:05 pm
content: Quote from: joeqsmith on July 07, 2025, 12:54:55 pmNo point in doing that, Im 100% sure the RL will be close to 0 dB, basically full reflection. its almost feels like checking that 2+2=4And there is no question about teflon+short - your result in this case was correct, the question is about two-port case.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 07, 2025, 02:10:26 pm
content: Quote from: yl3akb on July 07, 2025, 01:34:05 pmIn the 2-port case of measuring S21, I show a 10dB fixed attenuator as well as inserting a shorting plate between the two transitions as a sanity checks. Both measure as expected. If you have another test in mind, write it up and I can possibly attempt it.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 07, 2025, 02:43:50 pm
content: i used to take care of a Tan D setup for my former employer that ran from 200' c to Ln2 temperatures and 1 Mhz - 20 Ghz, Specifically for characterizing polymers.Tan D (a way to qualify loss on a single wave cycle) gives you a way to find Tg (Glass transition temperature) in polymers without a melt.I'm trying to remember the details from 18 years ago.Split Cylinder Loss cell is one of the tools you are looking for.https://www.electronics.org/sites/default/files/test_methods_docs/2-5-5-13.pdfCheck the references in 6.2 of the above for cell construction.Our machine had a variety of cell designs and an Agilent VNA running in a rack under external software control and a wide variety of cells. But just putting a chunk of polymer on one plane of a wave guide is out of the question. Even the surface finish of the test sample matters.Ah, Everything you never wanted to know on one way of making the cell, plus standard materials:https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote1354.pdfBringing it back to why this is a great topic for EEV Blog:https://www.isola-group.com/wp-content/uploads/Improved-High-Speed-Low-Loss-Materials-for-Lead-Free-Assembly-Compatibility.pdfWhen I get off shift, I'll see what I can find in a more "hacker friendly" cell design, I know they are out there.Ah, and here you go:https://www.electronics.org/sites/default/files/test_methods_docs/2-5_2-5-5-5.pdfThe above is not a Bereskin loss cell, but it is affordable.More PCB manufacturing related tests:https://www.electronics.org/test-methodsSome of those are damn interesting. Select the "Approved" link.Steve

author: yl3akb
author_rank: Regular Contributor
timestamp: July 07, 2025, 03:15:02 pm
content: Quote from: joeqsmith on July 07, 2025, 02:10:26 pmOkay. At this point its just for funCan you measure your WR90 adapters pressed together but with 5mm offset along the height (along the electric field direction). Just bare WR90 adapters, no dielectric, just for checking if we get the same result then. It is important that there are no gaps and no offset along width.See the simulation model and result at 10 GHz in attachment.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 07, 2025, 03:26:48 pm
content: Oh, even better way to make a quick cell.https://www.electronics.org/sites/default/files/test_methods_docs/2-5-5-10.pdfIt is a calibration short with a thinned down polished center pin making a capacitive cell.I'm liking putting the sample between the flanges. Just watch out for fringing fields if the sample is too thick.Steve

author: joeqsmith
author_rank: Super Contributor
timestamp: July 07, 2025, 04:17:02 pm
content: Quote from: yl3akb on July 07, 2025, 03:15:02 pmI don't have any application for it, so it's all been just for fun. So no worries about wasting time.I'll run your offset test tonight using the two transitions shown. Keeping in mind these are not good quality and will cause errors in the measurements.https://youtu.be/xe4Fy4Lpnqw?list=PLZSS2ajxhiQCyzRPSGkWSWfboP-5MfqWF&t=2117We have some known non-filled PTFE. I'll make up a second sample and see if it behaves any different. I'm pretty sure that first sample was non-filled as well.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 07, 2025, 04:49:42 pm
content: HP paper showing a sample brick inside rectangular waveguide. Decent paper.https://hparchive.com/seminar_notes/a-206.pdfJPL with their simulated Mars dirt. That's some large WG compared to my little WR90. Sample introduction is similar to what I did with my EPR experiment.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2025, 01:31:21 am
content: Made a new sample from some known unfilled PTFE. This is about 12.9mm thick. No X-acto this time, tighter tolerances and better finish.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2025, 01:32:31 am
content: Machined a simple step gauge to get the 5mm of offset.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2025, 01:52:58 am
content: This time I pinned the parts to align them and clamped them together. For S11 I show the shorting plate and load after cal.I then show the shorting plate and the mismatch load. I also show the transition to the load with a 5mm offset. I do this rather than using the crappy transitions to try and remove some of the error. Also shown is the transition and load with the Teflon inserted.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2025, 01:59:22 am
content: For S21, I used my one good transition. Shown are the thru (transition to transition), the fixed 10dB attenuator and the new Teflon inserted.Now why this new sample block, which is about two times thicker, has a lower insertion loss, I'm not sure. It's possible the original sample is filled to get the material more stable but it cut fairly easy with the X-acto knife.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 08, 2025, 05:14:22 am
content: Quote from: joeqsmith on July 08, 2025, 01:52:58 amThanks for the tests, your setup looks good! In case of 5mm offset test I see about 1 dB difference between simulation and measurement. I don't know why, but I guess that's the order of discrepancy we should also be expecting when comparing Teflon tests.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 08, 2025, 05:27:06 am
content: Quote from: joeqsmith on July 08, 2025, 01:59:22 amIn my opinion the explanation of lower loss in case of longer sample is simple. Length of the thicker sample is closer to half wavelength resulting in impedance transforming back the to original, unfilled waveguide impedance. You know, one full rotation in smith chart.Simulation with 12.86 mm sample also shows similar result at 10 GHz , although in case of S11 there is still about 1 dB discrepancy, and I dont get that 'peaking' characteristic like you got in your S11 graph.p.s.By there way, I guess the deep notch I got in simulation at 9.2 GHz may be exact half wavelength point. You may 'catch' similar response if you increase the span of your measurement.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2025, 01:53:27 pm
content: Quote from: yl3akb on July 08, 2025, 05:14:22 amWell, we are looking at pretty much a home made setup at a very low cost point. Maybe one of the members with access to high end equipment will care to repeat the test.QuoteI think I need to revise my previous statement and say that it depends what the makeup of the material is. That was a pretty significant change.I do have a thin sheet of Teflon that I could try to use but I would need to come up with some way to mount it inside the waveguide.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2025, 04:03:10 pm
content: Quote from: yl3akb on July 08, 2025, 05:27:06 amThe Agilent uses a PN# 11664-20021 1/4 wavelength shim as part of their calibration kit. This shim is 9.78 +/-0.02mm. I made a offset short as well as a shim that I use for calibration. I had purchased a 3/8 wavelength standard which is 14.48mm that I also use for verification.I would imagine if I stuff that Teflon inside that 1/4 wavelength shim, we will see a similar dip at 10GHz (within my ability to control the mechanical tolerances).I wonder if that was what they did with that paper..... Then again, lack off coffee, could be total BS...

author: yl3akb
author_rank: Regular Contributor
timestamp: July 08, 2025, 07:31:37 pm
content: Quote from: joeqsmith on July 08, 2025, 04:03:10 pm1/4 wavelength dielectric section would transform the impedance furthest away from nominal impedance causing the most reflection. It would look like slight dip in S21 graph.Also, it would not be as simple as filling that 1/4 shim with dielectric, because dielectric changes the cutoff frequency of that section (and guide wavelength as a result) so filled shim would not be 1/4 long.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 10:47:37 am
content: Quote from: yl3akb on July 08, 2025, 07:31:37 pmStay with me as I spin a non-coffee fueled story (it IS a story). First, I expect everyone reading fully understands where the 1/8, 2/8, 3/8 shows up on a Smith chart. There's no need to go over that. I was thinking about that paper you linked and the photos of their sample holder and the odd resonance at 10ish GHz (attached). Their text is pretty sparse, but it looks like two vintage HP X transitions. Now, when I look at the sample holder relative to the inner dimensions of the WG, and the size of the HP transitions, it sure looks like they used a standard 1/4 wavelength shim. There is a serial number marked on that shim, so I would not be surprised if that is not actually a calibration standard.So, here is my leap of faith in the author's as I can't wrap my head around the data they present. Let's just assume for now that they did not fudge the RL curves. I imagine (no data) they would have gone through a full 2-port calibration using the two HP transitions, then grabbed their offset shim, started inserting the samples and collecting the data. As the sample gets thicker, the notch starts to shift in frequency, sharpens and deepens.What I want to do is run through that little exorcise and see if I see this same effect. Again, I have no clue what they actually did or what parts they used, or even if that data they present has any meaning what so ever. This is where the thin PTFE sheet stock I mention comes in and how to mount it. I can pretty much guess that they just stuck it in there it was slightly oversized enough to stay in place. Note in that photo, the two transition are stacked vertically on a table. I assume the samples were tight enough to stay in-place and not fall into the lower transition during their test.My plan is to repeat my S11 measurement the same way as before and first make sure that everything replicates. As before, rather than two transitions I will be using my one good part and the Narda load to avoid errors of the poor quality parts from the university training kit. I had cut out a few inches of the Teflon from that same block. My one photo shows about 3" remaining. Now that we have some material that somewhat behaves, I plan to section that up to get a few different thickness samples. The goal is not to make their 1mm increments, but rather just some random 4 or 5 parts, including the part I previously used. Then shove them into my homemade 1/4 offset shim and measure them.If the goal is to explain what that paper is showing, maybe replicating it will provide some insight. Again, my homemade setup could be filled with errors. This is really a job for someone with an actual VNA. But as we have now stated, this is just for fun.I plan to make the samples today but doubt I will have time to run the test.***Before someone calls me out of the 1/2 wavelength typo, corrected to 1/4. Fixed a few grammar problems...

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 10:52:37 am
content: QuoteOne thing to consider is that the shorting plate only has the facing surface where the offset shorts or shims all have walls and will have additional loss. Tiny, but it's there.

author: ftg
author_rank: Frequent Contributor
timestamp: July 09, 2025, 01:12:34 pm
content: Quote from: joeqsmith on July 09, 2025, 10:47:37 amThat's the thing, they measured asample, not samples.The only sample actually measured is the 4.0 mm thick one shown.Then they used that measurement to derive some parameters of the sample and used those in a simulation for the other thicknesses.So I would only consider the curve for the 4.0 mm thick sample. As all other numbers are derived from that, not from measurements.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 01:30:50 pm
content: That one sample shows a notch at 10GHz. Mine started to peak up. Will it replicate when inserted into a 1/4 wavelength shim?

author: yl3akb
author_rank: Regular Contributor
timestamp: July 09, 2025, 02:16:04 pm
content: Quote from: joeqsmith on July 09, 2025, 10:47:37 amI dont see how 1/4 shim would make any difference, after all its just homogenous continuation of same waveguide and would only affect the phase, not amplitude.I just dont believe their RL graphs can be replicated with simple dielectric section. First of all why are they showing double notches (or one peak, that does not move in frequency)? And why 1mm thickness has such poor RL? At least in simulation, I see completely different results...

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 02:59:57 pm
content: Quote from: yl3akb on July 09, 2025, 02:16:04 pmAs far as ALL of your questions, I don't have any idea what is going on. Maybe there is something else I have not considered. I can't explain why I see such a peak at 10GHz.The Narda mismatch standard I have is actually a sliding load. Think of it as a load with an adjustable length of waveguide. I started to write software that supports it but the errors were so small compared to my poor man's setup, I abandoned it. Adding the shim is basically the same as adjusting that offset load. I would not expect there to be a difference.But, as long as it's just for fun and these tests are simple to setup and require no major effort to run, may as well have a look. Who knows, maybe I will see some double notch...Quotehttps://www.microwaves101.com/encyclopedias/sliding-load

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 06:09:55 pm
content: New test samples made from same stock.Left to right, sample 1 to 51) 2.40mm2) 4.15mm *3) 6.24mm4) 9.49mm5) 12.86mm* Very close to what was used in the paper.I repeated the calibration and once again measured the short, load and mismatch load. The mismatch load was measured fully extended and compressed.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 06:12:07 pm
content: Next I inserted the 1/4 wave shim between the load and transition.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 06:17:10 pm
content: Next I inserted sample #5 inside the transition and load. Again we see a similar peak as before. I suspect mounting the sample inside these two parts used to calibrated the VNA is causing the problem. It's not what the author's did anyway so I think it is safe to ignore this.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 06:22:34 pm
content: Next, using the 1/4 wave shim, I inserted each sample 1-5, measure them. After removing each sample I remeasured just the transition, shim and load with no sample to get an idea of how repeatable the measurements were. We are down in the muck, and while I am pinning the parts to align them, I am not bolting them together. Close enough.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 06:27:01 pm
content: Showing S11 for all five samples. Note only the original long sample #5 is not flat. It's the only sample that extends beyond the 1/4 wave shim. Also notice that the thinnest sample #1 seems to be an outlier. This part is so thin it is hard to get it to stay in place and remain flat.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2025, 06:34:19 pm
content: Looking at samples 2 and 3, 2 again being close to what was used in the paper, I repeated the measurement. Results were very similar. Also, very close to the paper's published RL. Still, I measure less than 1dB difference between the 4 and 6mm samples where the paper suggests about 4dB.

author: coppercone2
author_rank: Super Contributor
timestamp: July 09, 2025, 08:58:31 pm
content: For flattening stock I am tempted to build like a sandwich press so it can be thermally flattened. It would need 2 cartridge heaters and 2 metal pucks .Thin materials are very annoying to work with. A hot plate with a metal block might do it if you warm it up firstthey must have special tools for dealing with soft dielectric windows

author: joeqsmith
author_rank: Super Contributor
timestamp: July 10, 2025, 12:33:08 am
content: Showing samples 2&3 swept from 8.5 to 11.5GHz, along with the shorting block and load. Again, I'll be the first to admit this a very janky setup. But, still I don't see a pronounced dip near 10.5 and 11.5 as suggested. Hiding in the ripple or just not there.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 10, 2025, 05:58:03 am
content: Quote from: joeqsmith on July 09, 2025, 06:27:01 pmThanks for the measurement, good stuff.Your results look like whats expected - thinnest sample got relatively low reflection (because closer to zero thickness it is, closer to 'transparent' it gets - completely opposite, whats shown in paper), then peaks at 6..7 dB as it crosses the 1/4 guide wavelength and again reduces as it crosses 1/2 wavelength. If thickness would be increased further the pattern would repeat.For reference, i have attached simulation with your sample thicknesses. Tried to match axes range to your plot for easier comparison. You see its quote similar (expect #5, I got no peaking, but you said, that it may have been setup issue, and #1 got 2 dB discrepancy)

author: yl3akb
author_rank: Regular Contributor
timestamp: July 10, 2025, 06:02:40 am
content: here is wideband picture of same simulation, with frequency span same as shown in paper. Completely different picture. Okay we may ignore the band edges, due to real life finite bandwidth coaxial - waveguide transitions and calibration, but still, I got no peak at ~11 GHz...

author: joeqsmith
author_rank: Super Contributor
timestamp: July 10, 2025, 07:45:31 am
content: Quote from: yl3akb on July 10, 2025, 05:58:03 amUsing one of the low quality tuners from the university training kit, I backed the stub all the way out and attached the load and good transition as shown. I am using a more flexible coax so we can lay it on it's side, so it had to be calibrated.Next I insert sample #5 into the slotted line, near the load (8cm). I then moved it towards the transition in increments of 1cm. Basically Sample #5 was well behaved, until it approached the transition, eventually resulting in that same peak.I believe the setup when using the 1/4 wave shim and the longest sample #5 where it was allowed to extend into the transition was the problem.***The #1 sample was difficult to work with as it wanted to bend and not lay flat.We are working with a tiny fraction of the budget used to create that paper you referenced with a quarter the man power (8 authors), and getting completely different results. You could write the corresponding author of the paper and ask them for feedback.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 10, 2025, 02:14:06 pm
content: Sample #5 inserted into the slotted waveguide as before, but using a frequency range of 8.7 to 10GHz. I then moved the sample from 2.8cm to 3.3cm which does have an effect. The notch appears a bit high (9.5GHz vs your simulation around 9.25GHz) but it is there.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 10, 2025, 02:35:24 pm
content: For fun, shown is sample #4, inserted into the slotted waveguide, sweeping from 10 to 12.5GHz. No attempt was made to calibrate the system. I just wanted to see if there was any sort of a notch in this region like your simulation shows.

author: yl3akb
author_rank: Regular Contributor
timestamp: July 10, 2025, 05:09:04 pm
content: So basically considering all the limitations, errors and approximations (noticed that my simulation had PTFE model with constant er=2.1, but quick search showed that it may actually be ~2.05 at microwave, which would explain slight frequency error of those notches) we know what's the behavior of teflon section inserted into a waveguide and that the actual results do not match with what's in the paper.No, i will not write them, but knowing that EEVblog forum indexes well in search engines, someone researching similar topic (or after reading that paper) may stumble upon this thread

author: joeqsmith
author_rank: Super Contributor
timestamp: July 10, 2025, 07:02:19 pm
content: The LiteVNA doesn't perform very well above 3GHz, and 12.5GHz conversion is a bit of a stretch. If you like, I could calibrate the system and try and get a better picture of what is happening in that region.I do wonder what went wrong with their experiment. There's certainly a lot of room for error.Quotehttps://en.wikipedia.org/wiki/State_University_of_JakartaThis may explain some of what you are seeing.How did you come across that paper in the first place, and why did you decided to post about it?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 10, 2025, 11:14:43 pm
content: Showing sample #4 dip at 12.15GHz after calibration. There is definitely a notch as the model predicts, but the frequency is higher. Also, again, we are at the extreme end which is why there is so much noise. No self respecting university is doing this on a $1200 budget.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 11, 2025, 12:59:40 pm
content: Calibrating with the LRL training kit's transition, then attaching the LRL load and slotted line with sample #4. Both the load and transition have poor quality. The sources supplied with the kits operated at roughly 10GHz. We can see the notch near 12GHz but even with 10 averages, it has a lot of noise. I would imagine that we could easily run sample #5.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 14, 2025, 07:37:21 pm
content: Global Page (Click on Accepted Tests)IPC TM-650 Test Methods Manual | electronics.orgClip Method:https://www.electronics.org/sites/default/files/test_methods_docs/2.5.5.2a.pdf2 Fluid Cell Method:https://www.electronics.org/sites/default/files/test_methods_docs/2.5.5.3c.pdfStripline Methods:https://www.electronics.org/sites/default/files/test_methods_docs/2-5_2-5-5-5.pdfhttps://www.electronics.org/sites/default/files/test_methods_docs/2-5_2-5-5-5-1.pdfParallel Plate:https://www.electronics.org/sites/default/files/test_methods_docs/2.5.5.9.pdfSPLIT CELL (NIST)https://www.electronics.org/sites/default/files/test_methods_docs/2-5-5-13.pdfTDR:https://www.electronics.org/sites/default/files/test_methods_docs/2-5-5-7a.pdf

author: coppercone2
author_rank: Super Contributor
timestamp: July 14, 2025, 08:15:07 pm
content: I just found it interesting that sulfur can be molten and poured and it has a dielectric constant bigger then most plastics. Acrylic is 3.5 and sulfur can be up to 4.I wonder if I can fill a small section of wave guide with sulfur on a hot plate without having to do anything related to cutting