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Radiation patterns and loss of antennas operated well below resonance
Joel Koltner wrote:
Hi Richard, Thanks for your help... "Richard Clark" wrote in message ... Because they look cool? More because they don't take up a lot of space. I realize that any reasonably small antenna for 2m (meaning: "fits in the palm of your hand") is going to be a compromise anyway, but if you can have a nice-looking antenna that performs as well as a rubber ducky, heck, I'll have it look nice too... Stated that way, it should be possible to create a patch antenna that has comparable performance. Or a "patch looking" antenna. There's a couple ways to go about it, none of which involve starting with a 2.4 GHz patch operated at 1/20th the design frequency. 1) use something as a dielectric that has a high epsilon, so the wavelength is shorter. For cellphones and the like, various ceramics like alumina are used. It's pretty easy to get to epsilon=10, but that only gets you to 1/3 the size. 2) build something like a meander line on a suitable substrate. This is sort of the squashed flat version of a rubber ducky loaded vertical. Rather than making a 3d spiral which is a "radiating inductor" you do it on a flat surface. It's a bit tricky because a simple back and forth in a single plane won't radiate very well (the field from one meander cancels the adjacent one). But a spiral might work. 3) low loss lumped loading components. But, to return to your original 2.4GHz patch.. it's going to look like a capacitor of some sort at 144 MHz. The feedline would probably do most of the radiation. |
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