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what happens to the gain of a parabolic antenna, say this, http://www.amazon.com/24dBi-Directional-Booster-Parabolic-Antenna/dp/B00NQGVMSE, for example if I use it in lower or higher frequencies?

more specifically: what will be the gain if I use it in 1.1GHz, 1.5GHz, 1.9GHz, 3GHz, 3.5GHz?

will it even work?

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The antenna feed is designed for 2.4 GHz, so performance at other frequencies will be not good (unmatched impedance, poor gain).

The parabolic reflector is usable at other frequencies as long as the wavelength is not smaller than the grid spacing.

You can calculate the gain of the reflector at other frequencies.

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  • $\begingroup$ Thank you. If I was to pick a directional antenna that works in a wider band of frequencies, around 2.4, what would be your recommendation? $\endgroup$ – Nir Regev Mar 25 '16 at 18:34
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A parabolic antenna consists of two parts:

  • the parabolic reflector
  • a feed antenna at the reflector's focus

The feed antenna is commonly a horn antenna, which can have a relatively wide bandwidth, depending on the particular design. You will want to check the antenna's specifications. If the feed antenna won't work at your desired frequency, then you can replace it for one that does and keep the reflector.

The gain of a parabolic antenna is:

$$ G = {4 \pi A f^2 \over c^2} e_A $$

where:

  • $A$ is the area of the reflector in square meters,
  • $f$ is the operating frequency, in Hz
  • $c$ is the speed of light in meters per second, and
  • $e_A$ is the aperture efficiency.

This equation suggests that gain increases with the square of frequency. While this is technically true, it is intuitively misleading. The reason is that the free space path loss also increases with frequency, and as it turns out, the frequency term in the path loss equation cancels the frequency term in the path loss. So for a given power transmitted, the same fraction of power is received at the other end, regardless of frequency. There is no inherent advantage to higher frequency.

What you do get with increasing frequency is a decreased beam width for the same reflector. This has some benefits:

  • The Fresnel zone is smaller, so trees and terrain in the way is less of a problem
  • The decreased beam width can make it easier to reject interference that is near the same direction as the intended target

It also has some disadvantages:

  • It's harder to aim the antennas
  • Higher frequencies tend not not penetrate buildings, trees, etc. as well
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For 2.4 ` 2.5GHz antenna. You must be clear that it is a free band antenna. As for 3 Ghz to 3.75Ghz it lies in Paid frequency band. Other than this, For 2.4GHz yes you can use it with all the nearby frequency although it will hinder some of the gain issues but in practical scenario. It will work.

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