How Antennas Radiate
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- Опубліковано 27 лип 2024
- The mechanism behind radiation including explanation of the term radiation resistance. This video deals with a single current segment or area, not an array of elements or current maximums.
The radiated field varies directly with current integrated over a length of space, and the cosign of the angle from the antenna direction.
This video demonstrates that a long length of conductor wound up, bent up, or packed into a given linear space has no different radiation coupling than a single straight conductor occupying the same spatial distance so long as current distribution is the same.
What matters for radiation is not how much wire we pack into a length of space, but rather how we distribute the integrated or effective current over that spatial distance.
This video is not to endorse or discourage any particular design. Designs are a necessary mix of multiple compromises.
Part of transferring energy is power factor correction. Reactive power, or the volt-amperes reactive, also leads to losses or coupling problems. Radiation resistance and current distribution is just one part of a complex problem.
This video makes three important points I'd like everyone to take away:
1.) Antennas radiate all of the power applied, less the power lost as heat, regardless of size
2.) Radiation resistance in a simple small antenna is all about the current distribution and spatial length of the radiator in fractions of the wavelength
3.) People call antenna things they are not either by mistake or as an effort to "fluff up" something that is not really special
I hope to find time to go through various antennas and explain how they actually work and what they really are. - Наука та технологія
Tom , please continue to make videos like this. Most Ham videos on youtube are geared for people who don't wana know about how things actually work. Enjoyed the Beverage video as well. Have you ever tried a long beverage on 6 meters ? That was really good gain you were getting at HF . I wonder if it would work on 6 meters . Thanks again .
It’s one thing to be an expert in one’s field, it’s truly a gift to be able to articulate knowledge in such a way that others easily comprehend. Thank you! de NJ2US
You are a fine narrator Tom and an excellent tutor/elmer as well! Absolutely fantastic job which you must continue!
Thanks Takis!
What a privilege is to listen to you!
Many thanks!
Continue the good work Tom, very educational.
thanks for taking the time to make this, looking forward to your future videos.
Thanks you Bob. Nice hearing from you!
Excellent presentation and very thought provoking.
There really isn't anything thought provoking about it. Behind all EM radiation we have accelerating charges. Charges in motion produce strong local magnetic fields, charge distribution differences produce strong local electric fields, both of which decay rapidly with distance, while charges acceleration over linear spatial distance produce the weak local EM radiation that goes on forever at great distances.
@@Jerrythenerdful, I meant regarding the physics that cannot be defied by small antennas.
@@g0fvt Exactly.
There are a lot of magical small antennas, some made magical by calling them a magical name. In the final analysis, when we get past the fiction, there is no magic at all. Antennas all work like they should work. Make them smaller and the current has to increase to radiate the same power. Along with that at some place in the system the voltages get a lot higher, and there goes the efficiency. You can pack 10 miles of wire in a two foot space and it is still a two foot antenna.
@@Jerrythenerdful, on a tangent a little, from models it looks like there is benefit in making a "quarterwave" vertical fed against ground a bit on the long side and using a series C, would be interested in your assessment. It looks like it ought to have a better pattern for low angle and a "better" impedance. 73
Thank you for the valuable content here and on your site. Know that I could understand many things after reading the articles on your site. Thanks.
Very informative video and very interesting topic, (antennas). Once heard it stated that antennas may only rival the Bible in misunderstanding. Near field, far field nexus is critical. Abraham - Lorentz "Force" spells that out and makes most sense to me. A recoil force caused by acieration of a charged particle and pushes back on the wire. Near field rapidly diminishes inverse/cube of distance, far field inverse/square. All this zany stuff theorized about the same time Babinet came up with that light diffraction revelation basis for that "slot" . All fascinating stuff that keeps an old man awake at night but who cares, I'm retired and can sleep in the day. Keep up the good work ! FB...
73'
de K4WRF
Thanks for all your work !!
Very good. I would like to see more of these accurate videos. It would be nice to have video links to send newcomers that make sense.
Would love to see a video on correct antenna installation ! i. e. What interferes with antenna radiation! What kind of material should be used for low interference installation’s ! JohnBoyUtah KJ7TBR
Loved the video. Guess I can figure your view on a skeleton slot antenna. Thanks for sharing.
The skeleton slot is by definition not really a slot at all. It is an elongated loop. The in-phase current at the two current maximums that is additive in radiation broadside to the element is confined to the wide spaced short ends.
The long sections contain out of phase currents not only between sides, but between each part of a side. Not only is current out of phase, it also contains the current minimum. Any full wave loop is really just two short dipoles, end loaded by bending and fed in phase through direct coupling from end-to-end at the voltage points.
To be a slot antenna the current has to be excited in a wide sheet by impressing voltage across a slot or channel cut in the sheet.
Now with a stretch of the imagination we might consider the element a skeleton of a sheet, but with no sheet to have currents in that is a stretch saved by the word "skeleton:". We might just as well call a dipole a skeleton slot dipole, because it also is the "sheet less" complement of a slot. As a matter of fact analysis of current is a slot antenna are so difficult the mirror or complement is used to approximate or explain the pattern.
If we read Kraus and a dozen others we never see a slot without it being a slot. We find loops and dipole called what they are in an accurate descriptive way, not some fancy fake name. None of this changes how the antenna works, however. We can call it anything we like and it works the same. There is no magic.
Thanks for sharing.
Very good as always! Thanks for sharing. 73
Wish Tom would do mire videos. He ys a walking encyclopedia of rf knowledge...., 73 , N8QZH