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Yagi-Uda antennas are widely used in communication systems for their high gain and directivity. Calculating these parameters helps in designing effective antennas for specific applications. This article explains the basic methods to determine gain and directivity in Yagi-Uda antennas.
Understanding Directivity
Directivity measures how focused the antenna’s radiation pattern is in a particular direction. It is calculated by comparing the maximum radiation intensity to the average radiation intensity over all directions. Higher directivity indicates a more focused beam.
The formula for directivity (D) is:
D = 4π × (Antenna gain pattern)
Calculating Gain
Gain combines the antenna’s directivity with its efficiency. It indicates how well the antenna converts input power into radio waves in a specific direction. Gain is expressed in decibels (dBi).
The typical formula for gain (G) is:
G = Directivity × Efficiency
Efficiency accounts for losses in the antenna components. For Yagi-Uda antennas, efficiency is usually high, often above 80%.
Estimating Gain and Directivity
For practical calculations, the directivity of a Yagi-Uda antenna can be approximated using the number of elements. A common approximation is:
D ≈ 10 × log10(N)
where N is the number of elements in the antenna. The gain can then be estimated by multiplying directivity with efficiency.
- Count the number of elements in the antenna.
- Estimate directivity using the approximation formula.
- Multiply directivity by efficiency to find gain.
- Express gain in decibels (dBi).