Inside Wireless: VSWR, |S11|, Return Loss

[@Rfelements]

What is acceptable matching level in your industry?

[@Tom-dn5de]

Thanks for the great video! and I have some things to ask. The frequency of the reflected signal is the same as the frequency of the feeding signal or a little difference? And how about the relative phase between them?

[@Rfelements]

@@Tom-dn5de Yes, frequency is the same, unless the signal reflects from some non-linear circuit or what not, then it can be different, but for antennas are linear. The relative phase can be calculated exactly depending on the transmission line length, but for practical life VSWR is more useful since it gives information on the steady state. If you're interested in transient phenomena, then the relative phase can be interesting for you.

[@Tom-dn5de]

@@Rfelements Thanks for your explanation, I'm making an output impedance measurement of an RF signal generator using an RF spectrum analyzer, an auxiliary RF signal generator, and a directional coupler. I don't know why an auxiliary generator is used which transmits a wave with a slightly offset carrier frequency into the DUT. This method makes me a lot of confusion. I'm not good at RF but always want to learn about it. Could you explain it to me? This method is from euramet on page 16. www.euramet.org/index.php?eID=tx_securedownloads&p=529&u=0&g=0&t=1653590394&hash=968b4e5de0234a96189d8595ea66236a3bc8b6f5&file=Media/docs/projects/EURAMET-P1461_EM_Final_Report.pdf

[@Rfelements]

@@Tom-dn5de The generator impedance measurement is done indirectly through the setup that's described in the pdf. The measurement signal is AM signal. The generator impedance is derived from the reflection coefficient of the modulated signal.

[@Tom-dn5de]

@@Rfelements Thanks for your great help! I appreciate it.

[@evilhacker8272]

The video is short, but absolutely gold. Thank you.

[@yassersultan1467]

thanks to my genius professors I was struggling to understand what vswr is , this video helped me to understand it thank you soooo much

[@zoewu8839]

Thank you for sharing the knowledge. Really helpful!!!!!! You are absolutely so cool

[@ElectronicsCuriosities]

Every clear and informational. Thank you 👍

[@Rfelements]

Glad it was helpful!

[@sushantgupta4757]

Thnak you so much for saving my project

[@mndsaini01]

every word of this video is treasure

[@mdhalimakhtar447]

Wow great explanation

[@Jota_VA]

Awesome animations, thanks for sharing. Scattering parameters and libre VNA would be great. Regards.

[@chupick94thebest]

Great video!

[@Rfelements]

Thanks!

[@cenonlumabadiii8976]

I've seen technician measuring VSWR in the link when they installed wireless communication system.Given that every parts is fixed, why would they bother measuring the VSWR? And if if it's poor, what to do to improve it?

[@Rfelements]

It makes sense if the gear is expensive - you rather check everything well before you turn the system on. In the worst case, the reflection from the load (cable plus antenna and anything in between) can burn the signal source (unless it has some protection in place). If the VSWR is poor, then you have to check each component separately, figure out which one is not matched well and either tweak it or replace for a better matched one.

[@cenonlumabadiii8976]

@@Rfelements Thanks for your time to explain it, I teach engineering subjects so its helpful to learn from experts in the field. BTW, just a follow up questio. For practical purpose, does cutting the T-line a couple of cm or inch from Tx to Antenna have any adverse effect on VSWR? Or does if affect phase at the output?

[@Rfelements]

@@cenonlumabadiii8976 Cutting a cable shorter affects the phase, provided that the transmission line has the same connector and is not otherwise deformed - its characteristic impedance does not change with it being longer or shorter.. Oh, and also the insertion loss, naturally - the shorter the cable the smaller insertion loss.

[@cenonlumabadiii8976]

@@Rfelements Thank you again :) Your answer are far better than just googling these concepts!

[@Rfelements]

@@cenonlumabadiii8976 happy to help! :)

[@harlemespanol]

Great explanation! When choosing an antenna, what is more important, the lower the VSWR or the higher the antenna efficiency?

[@Rfelements]

That largely depends on the application, but generally speaking the smaller the VSWR, the higher the radiation efficiency of an antenna (unless there is a lot of loss within the antenna body, in substrate, or metal).

[@harlemespanol]

@@Rfelements I’ll be using a 5.8 dBi antenna for Helium mining.

[@harlemespanol]

@@Rfelements Antenna #1 - VSWR 860MHz 1.83, 930MHz 1.45 83%. Antenna 2# - VSWR 860MHz 1.9276, 930MHz 1.2889 66%

[@Rfelements]

@@harlemespanol VSWR < 2 is considered a level of good matching for most applications. The choice also depends on the distance you're trying to cover, radio output power, sensitivity of the receiver, and SNR requirements. Based on these you can do a link budget calculation that will give you a good idea if either one of the antennas is enough.

[@harlemespanol]

@@Rfelements Okay. Thank you for your insight.

[@ayhannkaraca]

Thank you sir.

[@zongyang779]

Very well explained

[@mohamedazzam6226]

Thanks for these useful videos, Can you make a video about CDF probability, please.

[@Rfelements]

Hi @Mohamed_Azzam, thank you for the tip, we'll look into it and might make one in the future!

[@OxTongue0]

Thanks for the video

[@Rfelements]

you're welcome!

[@dobirhossain3406]

Hi, good effort. But I think you didn't follow the right way to calculate the reflected power. Cause your input power is in dBm and RL (30 dB) is a unitless parameter. So, how is it possible to subtract a unitless parameter from a parameter that has a unit? Can you explain this, please?

[@bandaruramana2119]

I can because who told that return loss had no units it's there in db's so input power can get added if it is gain and subtracted if it is loss that's it

[@jinhojonathanng6188]

Thanks for the video!!!

[@payambakhshi1498]

I will appreciate if you can post videos about Downfade Upfade topics in multipath...thanks

[@Rfelements]

Thanks for the tip, we have bunch of videos in the pipeline, but are always looking for relevant topics for future videos!

[@wayofsalaf]

hi sir, how can u measure reflected energy= 11% if the vswr value = to 2? answer pls

[@Rfelements]

reflected energy is directly connected to vswr, so you only need to measure vswr, which any network analyzer does.

[@lacyrjoao2553]

Perfeito. Obrigado.

[@Rfelements]

We're glad you find this vid useful

[@harlizarazali481]

Why this video said the -20dB for S11 is already consider among the best value for antenna performance. Any reference to take as prove?

[@Rfelements]

Hi Harliza, in the video it says -20 dB is considered a very good level of matching, not 'the best'. The requirements on the level of matching vary from one application to another so it's all relative, but we can say that in the world of antenna engineering -20 dB is a pretty good one, considering it means 1 % of energy reflecting back to the signal source..

[@harlizarazali481]

@@Rfelements Thank you so much for your good explanation.

[@lizaaras7441]

nice interpretation

[@teguhpraludi2201]

so return loss , always positif and S11 negatif ? what is the meaning?

[@rhutabaga]

Hello, I'm looking at an antenna that is good on most of the frequencies it can use except for the one I'm interested in which 617-700, at 617 it spikes around 5 VSWR and eventually comes down to 2.5 VSWR at 680 mhz, should I purchase this antenna or pass on it? Thanks for the video, this helped more than the other sources I've been using.

[@Rfelements]

Hello. If the worst was 2.5 maybe you should consider it, but 5 is just too high. Thanks

[@rhutabaga]

@@Rfelements Thank you, that helps me a bunch, much appreciated.

[@michellemunoz5265]

hi what is the equation to get reflected energy= 11% if the vswr value = to 2?

[@Rfelements]

Considering linear scale, reflected energy = |S11|^2 = ( (VSWR - 1) / (VSWR + 1) )^2 = 0.111 for VSWR = 2. The power of 2 gets us from voltage wave amplitude to energy.. check this page for the formulas www.everythingrf.com/tech-resources/vswr

[@omanghana3291]

Please what should we do when the vswr is above 2.5

[@Rfelements]

Use a different antenna. If its specified VSWR is above 2.5, it's a poorly designed product. Generally, it depends on the application if 2.5 is too much. What application / frequency band are you considering?

[@bochraaassouss8854]

Thanks

[@YAHYAMOHAMMEDSINJABTMB]

dude u r amazing

[@leeBenny-t2k]

the equation is incorrect? How to use s11=-10 to calculate vswr=2?

[@yupitsallfun]

Why is |S11| in vertical brackets? It doesn't look like absolute value.

[@Rfelements]

Yes, it is an absolute value of S11..

[@rameshsaravanan877]

How to improve return loss

[@Rfelements]

improving return loss is about matching - the closer the impedance of an antenna to the feeding line, the better it gets..

[@rameshsaravanan877]

@@Rfelements thank you can you explain the one video

[@asgua5224]

The last moment vids for exam watching 1hr. Before exam😅

[@jeffm2787]

2:0 might be acceptable, but nobody really wants that big of a mismatch. 1.5:1 or less I'll take.

[@Rfelements]

Still depends on he application, really

[@Mundovariedad2]

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[@Rfelements]

Glad you find it useful!

[@colinikeooldridge1332]

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[@StbanSmite]

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[@SmithCalvin-d1x]

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[@melvinbradberry8729]

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[@jluke6861]

Great Video. Thank you.