Gain
Horns have very little loss, so the directivity of a horn is roughly equal to its gain. The gain G of a pyramidal horn antenna (the ratio of the radiated power intensity along its beam axis to the intensity of an isotropic antenna with the same input power) is:
For conical horns, the gain is:
where
- A is the area of the aperture,
- d is the aperture diameter of a conical horn
- λ is the wavelength,
- eA is a dimensionless parameter between 0 and 1 called the aperture efficiency,
The aperture efficiency ranges from 0.4 to 0.8 in practical horn antennas. For optimum pyramidal horns, eA = 0.511., while for optimum conical horns eA = 0.522. So an approximate figure of 0.5 is often used. The aperture efficiency increases with the length of the horn, and for aperture-limited horns is approximately unity.
Read more about this topic: Horn Antenna
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