Antenna Briefs #6 - Analysis, Simulation, and Measurements

This episode looks at how antennas are analyzed and simulated. It starts with real-world measurements to set the stage and illustrate key issues like antenna patterns. We then dive into some of the mathematical theory behind pattern formation. But as always, the focus is on understanding the theory that is relevant to engineering. Information on and examples of antenna simulation software products are also provided.
A few of the links shown in the video, plus a few related ones:
EZNEC Simulation Software:
www.eznec.com/
EZNEC Tutorial Video:
• EZNEC Antenna Software...
Tutorial paper on Method of Moments solving technique:
www.researchgate.net/publicat...
(See options in upper right of ResearchGate page for getting PDF or reading directly)
Excellent KZbin presentation of B-field origin (Thanks SaltyPuglord for this link !):
• How Special Relativity...
Textbook on EM with B-field discussions backing up what's said in video (see Chapter 5):
documents.pub/document/berkel...
KZbin video with EM field animation: • Understanding Electrom...
(Note: I think the Receiver loop in the Hertz demo at the beginning is 90 degrees off...)

[@dingdinglhz001]

I can't wait for your future videos! Working in a experimental physics lab, we sometimes need to build electronics (RF amps and antennas included) at non-commercial frequencies and with many constraints (like size). Your videos bridged a lot of knowledge / experience gap!

[@MegawattKS]

Many thanks. I got delayed working on the next video, but your comment helps motivate me to get it done :-) Thanks for taking the time to let me know they're helpful !

[@SaltyPuglord]

Thanks a lot for your hard work on these videos. I am really, REALLY enjoying them! The significant difference in impedance of a dipole caused by interaction with the coax feedline shield was a real mind-blower for me. I'm looking forward to the next video with lots of anticipation! I put this video up on Reddit at the /r/RFElectronics subreddit. I hope that's cool. If you don't want me sharing your videos there, let me know, so I can stop doing so.

[@SaltyPuglord]

For anyone who hasn't seen it: Veritasium's video on how length contraction caused by special relativity causes magnetic fields - kzbin.info/www/bejne/Z4WuhJl3oLyKhJI

[@MegawattKS]

Wonderful. Thank you! I had been looking for places to link them where people interested in this type of content might see them more, but wasn't aware of the Reddit RFElectronics group. Actually I don't use Reddit unless it turns up something in a search. But I'll definitely start now that you've told me about it. Thanks so much !

[@MegawattKS]

Just watched the Veritasium video. Wow - that's a fun presentation - and well explained ! Thanks for the reference !!

[@byronwatkins2565]

Length contraction; time dilation. Contraction is reduction in size; dilation is inflation in size. The time between clock ticks seems longer; the distance between nuclei (atom cores) seems shorter. We get exactly the same attractive force using either strategy so it doesn't matter who believes what. E and B are in phase IN THE FAR FIELD (plane waves); but, not in the near field.

[@MegawattKS]

Thanks for the correction. I didn't catch that one during my review and final edit. If you haven't seen it yet - SaltyPuglord has provided a link to an excellent video covering this too :-) And I just updated the Description to add that link plus one to a Berkeley Physics Course text on EM that details the description and the math behind it.

[@rjordans]

Thanks again!

[@johnbarber1482]

My professor doesn't even show up to teach... He's only done 5 lectures from 22 Aug to 31 Oct. I've learned more on two of your videos than 5 of his lectures. Thank you!

[@MegawattKS]

You're very welcome. Glad to hear they're helping - and sad to hear about the class. Hopefully the material aligns reasonably well. But I'm sure whatever the prof covers differs in some ways. Hope he covers enough for the tests/etc. In any case - enjoy the learning. Electromagnetics is a fascinating subject.

[@salehsalehi8955]

Thank You So much for your Video(s), I enjoy them immensely .. Best Regards

[@MegawattKS]

You're very welcome. Thanks for the feedback. It's good to hear that the videos are helpful :-)

[@samadams6487]

I do not see the KZbin link for the tutorial in the notes section/ description section

[@MegawattKS]

Thanks for the suggestion. I've added some links in the description. I think this is the one you're interested in ?: Tutorial paper on Method of Moments solving technique: www.researchgate.net/publication/260515353_A_Tutorial_on_the_Method_of_Moments (See options in upper right of ResearchGate page for getting PDF or reading directly)

[@Mahmoud-to6ws]

Doctor, I want to make an antenna to connect it to a terrestrial radar device that sends and receives waves with a capacity of 900 megahertz. Can you help? Please advise. Thank you.

[@danilo1782]

Dipoles are known to be only 2 dBi gain antennas. In this test we see two dipole antennas which make 4 dBi together. So why do they appear to lose many more than 4 dB when we change their position / polarity?

[@MegawattKS]

Agreed. The net transmit plus receive antenna gain is 4dBi in a traditional Friis path-loss formulation for received signal level. (In the slide at timestamp 1:15 , a different derivation is used, but it's equivalent to the Friis, with Gr accounted for in Leff) But to the question of why do we lose much more power when we change position / polarization, the answer is that the "2dBi" gain quoted for a dipole only applies when the antennas are broadside and co-polarized. If they are not, then a dipole has lower gain than 2dBi. Indeed, when we go from broadside orientation to "endfire" as shown in the video, we see a huge drop in received signal. One way to think about this is to look at the fields shown on the graphic at 1:15 . For good reception, the receive antenna needs to be parallel to the E field that is coming at it. If it is not, then less total voltage (Vr = E * Leff) is induced. From the geometry, it should fall off as cosine(theta) where theta is the angle between the E field and the antenna element. Does that help answer the question?

[@danilo1782]

@@MegawattKS thank you for your kind reply. I had thought that the phenomenon was due to the close proximity of the antennas which made the gain appear much stronger than normal.