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Patch antennas are commonly used in satellite systems due to their low profile and ease of fabrication. Calculating their gain and directivity is essential for designing effective communication links. This article provides a straightforward overview of the methods used for these calculations.
Understanding Directivity
Directivity measures how focused the antenna’s radiation pattern is in a particular direction. It is a theoretical value that indicates the maximum possible gain of an antenna assuming no losses. For patch antennas, directivity depends on the antenna’s shape, size, and operating frequency.
The directivity (D) can be estimated using the formula:
D ≈ 4π / Ω
where Ω is the beam solid angle in steradians. For a typical patch antenna with a known radiation pattern, Ω can be calculated based on the half-power beamwidths in the principal planes.
Calculating Gain
Gain (G) relates to directivity but also accounts for efficiency losses. It is calculated as:
G = η × D
where η is the efficiency of the antenna, typically between 0.6 and 0.9 for patch antennas. To determine gain accurately, measure or estimate the efficiency and directivity.
Practical Calculation Steps
- Determine the operating frequency and physical dimensions of the patch.
- Calculate the beamwidths in the principal planes from the radiation pattern or simulation data.
- Compute the solid angle Ω using the beamwidths.
- Calculate directivity using D ≈ 4π / Ω.
- Estimate efficiency η based on fabrication and material properties.
- Calculate gain as G = η × D.