What are Antenna Gain, EIRP, and Friis Equation?

[@eswnl1]

9:30 Just to make sure, I think the words "effective area" doesn't mean area of the beam. It means imagining an equivalent isotropic with its receiving area scaled up by Gr. The reason is that receiving area for directive antenna is undefined but it is defined for isotropic (lambda^2/4pi). Similarly, at the transmitter, the power density is undefined for a directive antenna but it is defined for a sphere (Pt/4pi d^2). It seems that we can only analyse when we work in terms of isotropics.

[@iain_explains]

Those quantities are not "undefined", but they are easiest to quantify with reference to the isotropic case.

[@joshroppo5136]

Thank you so much for this video! I've been trying to figure out what EIRP for context at work, and thanks to your wonderful teaching-via-diagramed-formulas it's starting to click!

[@iain_explains]

That's great to hear. I'm glad you like the approach I took to the explanation.

[@oak6302]

Thank you for this video. I just started an internship and had no idea what gain or the friis equation was but thanks to you I have a decent understanding

[@iain_explains]

Glad it was helpful!

[@muhammadissam3684]

I have never found a better explanation than this. Absolutely brilliant mind! God bless you friend

[@iain_explains]

Thanks for your very nice comment. I'm so glad you found the video helpful.

[@zhanggu2008]

concepts and relationships are explained crystal clear One question: Why is EIRP important in OTA testing? the last equation (P_out) does not contain EIRP.

[@iain_explains]

Yes, the last equation does contain EIRP. The first two terms on the numerator are exactly the definition of EIRP.

[@chakwachan1908]

This is very clearly explained! Thank you!

[@iain_explains]

Glad you found it useful.

[@kristhompson8112]

I am currently studying for my Ham Licence exam here in New Zealand, It's starting to sink in sort of. I am also a sailor , so in practical terms I make the parallel between what I already know with how a lighthouse " Fresnel lens" works to take the total energy (P= wattage) of a small bulb and focus it into one very tightly controlled beam that can travel many N-miles to the horizon, keeping us hopefully safer and on the right passage, Kind of the same, but different in that light doesn't bounce off the ionosphere like DX radio waves do.Oh and of course there is no gain in the human eye unless you have some night vision goggles or telescope eyes . LoL . Thanks for your video, expressing this physical / practical world I know and have experience in the real world in mathematical terms/ symbols and ratios is taking a leap of faith that is not easy for getting my brain around, or second nature for me. Math was not my best subject at school , but you breaking it down has certainly helped put me towards understanding a little more of the greater picture, and of course I actually want to understand what I am learning rather than just parroting off the answers. Regards and 73's Kris

[@kristhompson8112]

P.S is this why Ham radio opps express their signal RX receiving levels as a "S" reading , as you used a capital S in your equations ??

[@iain_explains]

That's great to hear, Kris. I'm so glad the explanation helped you. Your analogy to the optical case is a good one. Actually there is a "gain" in the human eye, since the area of the retina is smaller than the opening in the iris. The lens in the eye gives the "gain". This is similar to an optical telescope.

[@kristhompson8112]

@@iain_explains Thanks for coming back to us. Wow I've again learnt something new today, never thought about that physical ratio in that light (pun intended) before, but totally makes sense. Lol if only we had a tapetum lucidum at the back of our eyes, Great for when I'm looking through my Celestron Telescope at night but probs not so good during the day eh, Stay well and keep your wonderful vids coming I says. Regards Kris

[@maris6843]

Excellent explanation.

[@iain_explains]

Glad you liked it

[@akbarrahmatullah6701]

Could you do a video on TEM wave in lossless isotropic free space. An explanation of why the E field component and H field are in phase for an EM wave?

[@iain_explains]

Time varying electric fields and time varying magnetic fields exist together. They are both manifestations of the electromagnetic force, which is one of the four fundamental forces of nature. I think the best way to think of it is that if you generate a time varying electrical field (eg. by making the current in a wire change direction from positive to negative and vice versa, according to a sinusoidal wave), then it induces a time varying magnetic field that is by its very nature "in phase".

[@Julia-hu4xe]

Thank you, so the gain can be always determined by taking the ratio of either the squared voltages or the power. Is that right? Thanks.

[@iain_explains]

Yes that’s right. P=V^2/R so when you take a ratio of two powers, the resistance, R, cancels on top and bottom (since the resistance doesn’t change).

[@bandaralghamdi3176]

What an excellent explanation

[@iain_explains]

Glad you liked it

[@muhammadahmedtariq2357]

Can you illustrate difference between gain and directivity ?

[@iain_explains]

Thanks for the suggestion. I've put it on my "to list". In summary, the _Directivity_ deals with the shape of the radiated beam pattern (how directed it is, compared to an isotropic antenna). The _Gain_ includes Directivity, but also includes a measure of how effective the antenna is in transferring the energy in the EM wave, into electrical energy in the wires (for a receiving antenna, and vice versa for a transmitting antenna). This combined factor (directivity and effectiveness) is captured by the "effective area" parameter.

[@michaelalex5235]

At 5:39, is lambda squared the cross-sectional area?

[@eswnl1]

I wonder if the E in EIRP stands for "equivalent" or "effective"? Some texts use both. The word "equivalent" makes more sense because its how much power you would need to put in an isotropic to achieve the same level. Also there's ERP when using non-isotropic antennas, but EIRP makes most sense intuitively because isotropic has zero gain and it makes sense to reference other antennas to this. Also in EIRP, the gain must be in dBi.

[@Fz3r0_OPs]

Wow, very nice explanation. Thank you very much for the share!

[@iain_explains]

Glad it was helpful!

[@srb1855]

Really well done. 👍

[@iain_explains]

Thank you! Cheers!

[@UriahHeepBr]

Excellent video!

[@iain_explains]

Glad you liked it.

[@DarianCabot]

Very clear explanations, thank you! Please correct me if I'm wrong - but I *think* I understand why standards like AS/NZ 4268 define a maximum EIRP for a given frequency band. They are interested in real-world emissions, they don't particularly care how powerful the transmitter is, but more concerned with what is emitted in worst case (i.e. something in the path of the main lobe). AS/NZ 4268 points to EN 300 220-1 for measurement methods. I can't see reference to EIRP, only ERP. The measurement is to connect the transmitter to a dummy load and measured with measurement receiver (RF voltmeter or spectrum analyser), then the maximum antenna gain is added to this. In AS/NZ 4268 they state "ERP will always be 2.15dB less than EIRP". Does this mean we just add 2.15 to ERP to get the EIRP value? What is the significance of the "2.15dB" value? Sorry I got in the weeds a bit - I'm trying to learn this subject as a novice - so I really appreciate your videos! :)

[@DarianCabot]

Found the significance of "2.15". From Wikipedia's ERP article: "The difference between EIRP and ERP is that ERP compares the actual antenna to a half-wave dipole antenna, while EIRP compares it to a theoretical isotropic antenna. [snip] a half-wave dipole antenna has a gain of 1.64 (or 2.15 dB) compared to an isotropic radiator". From that I gather: EIRP = ERP + 2.15 (if in dB), or ERP = EIRP + 1.64 (if in W). Right?

[@iain_explains]

Yes, that's right. I'm glad it makes sense.

[@eswnl1]

I think what could have been included is how the Friis formula leads to the impression that lower frequencies travel further due to the presence of the lambda squared term. This is misleading as the lambda term determines the effective area where power from the wave is extracted. Propagation in free space is infact independent of frequency. The real reason lower frequencies seem to travel further is propagation mechanisms that are available to it that are not available at higher frequencies.

[@iain_explains]

That's an excellent point. And it's something that I continually have to explain to people. High frequencies travel to us from other galaxies, just like lower frequencies do too. So it's not that they don't travel the same distance! They clearly do (in a vacuum, anyway). Of course there is the atmospheric absorption, but that's really only a big effect at a couple of frequencies, otherwise it's a gradual increase with frequency. I think I'll add it to my "to do" list for another video. Thanks.

[@DRACOBUCIO]

Where can I find the derivation of 5:41? I really want to understand that tricky part.

[@pitmaler4439]

Thanks a lot, I know Ae is a theroretical quantity of an antenna and it depends of lambda. Is it really Independent of the antenna size? An array has the same Ae like a dipol - assumed both are for the same frequency made thanks

[@oldschoolfoil2365]

So EDRP and EIRP? gain is the result when two make contact? regardless of direction?

[@barendsmillylombard5487]

Great video thanks

[@iain_explains]

Glad you like them.

[@manolisangelakis1173]

Excellent!!!!

[@iain_explains]

Glad you like it!

[@user-lp2op9uu1w]

Amazing, thank you!😀

[@iain_explains]

Glad you liked it.

[@marksalazar7635]

hello sir! is there a voltage intensity in isotropic antennas?Thank you...by the way, very nice video. thank you

[@iain_explains]

Thanks for your comment. Sorry, I'm not sure what you mean by "voltage intensity".

[@marksalazar7635]

@@iain_explains thank you for the reply. actually that was a question of a student, i think it was from a Tomasi book. i also haven't encountered the term so maybe you had an idea..but anyway, thank you so much. by the way your explanations are simple and easy to understand...thank you

[@oldschoolfoil2365]

You mean voltage as in field size of the isotropic sphere frequency? yeah sure more juice bigger the sphere i guess

[@foryou7657]

I need your help please