# Tag Info

4

The aperture efficiency of a horn or reflector antenna is the ratio of the effective aperture to the physical aperture. The formula usually looks like: $$\epsilon_{ap} = \frac{A_e}{A_p}$$ The aperture efficiency is a dimensionless number usually reported as a percentage and $A_e$ is the effective aperture and $A_p$ is the physical aperture. For horn and ...

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If the only thing the material did was "reflect", and it was like a flag on a vertical antenna, then I guess it wouldn't have any effect on the radiation pattern. The problem is that no such material exists. One problem is that for a material to "reflect", it has to be many (at least 10, say) wavelengths long. Any less than this, and effects like ...

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If the transmitted signal induces any currents in the "sheet", the sheet will affect the radiation pattern. One simple argument: if you run a wire parallel to the "flag pole", there will be induced currents. They may be small (if the wire is not resonant) but there will be some current. (Think of how a yagi antenna works with its "parasitic" elements.) ...

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The aperture efficiency tells you what percentage of the power incident upon the antenna is available at the feedpoint. The concept of "power incident upon the antenna" is a bit weird. So let's take a step back, and consider something more visible, like a sheet of paper. At any time there's some amount of light hitting this sheet of paper. We can increase ...

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Much depends on the relative sizes. A metal flag on an HF vertical antenna is not likely to change the pattern in any way you'd notice. A gum wrapper near a 2.4GHz antenna definitely will change the pattern. I once did a design for a 2.4Ghz consumer product and ended up sculpting the antenna pattern with a block of nylon adjacent to the antenna, acting ...

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