Timeline for Why dimension of antenna's elements can be 1/2 and 1/4 or wave length and what about 1/3 or 1/8?
Current License: CC BY-SA 4.0
7 events
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| Feb 27, 2021 at 21:43 | comment | added | Math Keeps Me Busy | @Andyaka it may be a terminological thing, but when I see the term "half-wave dipole", I understand it to be a "resonant half-wave dipole", which is half an electrical wavelength, rather than half a free-space wavelength. It is slightly shorter (than the half a space wavelength), and has 0 reactive impedance. Similarly for a "quarter-wave monopole". I understand that to be a "resonant quarter-wave monopole", which will be shorter than a quarter of a space wavelength, and will have 0 reactive impedance. I can't think of a good reason to make an antenna an exact multiple of 1/4 space wavelength. | |
| Feb 27, 2021 at 19:55 | comment | added | Andy aka | You should still use the 0.5 lambda position for a quarter wave monopole and it reveals an impedance of 37 ohms + j21 ohms (basically you half the impedance values for a monopole) when using the graph above. | |
| Feb 27, 2021 at 18:00 | comment | added | Math Keeps Me Busy | @gavenkoa I am not sure about your formulae either, but they seem to be in the right ball park. I don't know the formula used in the graph I added. I might research it later today. | |
| Feb 27, 2021 at 17:51 | comment | added | Math Keeps Me Busy | @gavenkoa I added a diagram from Wikipedia that shows the rapid increase in capacitative reactance below 0.5 wavelength for a half-wave dipole. | |
| Feb 27, 2021 at 17:49 | history | edited | Math Keeps Me Busy | CC BY-SA 4.0 |
added diagram and explanation
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| Feb 27, 2021 at 17:02 | comment | added | gavenkoa |
Interesting note about capacitive reactance, I'm not sure about the correctness of my formulae interpretation but I see Xc=1/(2πfC) and capacity is proportional to the square or cube of linear size (depending on antenna's geometry): C=O(dim²) or C=O(dim³) so decreasing size two times may lead to 4-8 more reactance, with 1/8 it decreases 64-512 times and that might have an impact.
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| Feb 27, 2021 at 15:37 | history | answered | Math Keeps Me Busy | CC BY-SA 4.0 |