Calculate parabolic reflector antenna gain and beamwidth by entering your antenna's diameter, operating frequency, and efficiency. You get back the gain in dBi, half-power beamwidth in degrees, and wavelength — useful for satellite dish sizing, VSAT design, and RF link budgeting.
Antenna Gain
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Half-Power Beamwidth
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Wavelength
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Gain (Linear)
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Effective Aperture Area
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Antenna gain is the ratio of the signal power radiated (or received) by an antenna in a specific direction compared to an isotropic radiator that transmits equally in all directions. It is typically expressed in dBi (decibels relative to isotropic). Higher gain means a more directional antenna that focuses energy into a narrower beam.
The gain of a parabolic dish antenna is calculated as G = η × (π × D / λ)², where η is the efficiency factor (0–1), D is the dish diameter in metres, and λ is the wavelength in metres. In dBi, this becomes G(dBi) = 10 × log10(G). The wavelength λ = c / f, where c is the speed of light (3×10⁸ m/s).
Most practical parabolic reflector antennas have an efficiency between 50% and 70%. A value of 55–60% is commonly used as a realistic estimate for standard offset-fed or prime-focus dish antennas. Higher efficiencies up to 80% are possible with precision manufacturing but are less common.
The half-power beamwidth (HPBW) is the angular width of the antenna's main beam at the points where the radiated power drops to half (–3 dB) of its peak value. A narrower beamwidth means higher gain and better directivity — critical for satellite links where you need to point the dish precisely and avoid interference from adjacent satellites.
Gain increases with the square of the dish diameter. Doubling the diameter quadruples the gain (adds approximately 6 dB). This is because a larger aperture captures more incoming signal power and focuses the transmitted beam more tightly, directly improving link performance.
The Antenna Factor (AF) is defined as the ratio of the incident electromagnetic field strength to the output voltage at the antenna connector. It is inversely related to gain — a higher-gain antenna has a lower antenna factor. The relationship for a 50-ohm system is: AF (dB/m) = 20×log10(f) – G(dBi) – 29.79, where f is in MHz.
Higher frequencies produce shorter wavelengths, which means a dish of a given size achieves higher gain. Ku-band (10.7–14.5 GHz) and Ka-band (26.5–40 GHz) are commonly used for VSAT satellite communication because they allow compact dishes to achieve high gain. C-band (3.4–7.0 GHz) requires larger dishes for equivalent gain.
This calculator is specifically designed for parabolic reflector (dish) antennas using the standard aperture-based formula. For dipole, yagi, horn, or patch antennas, different formulas apply. The effective aperture approach used here is valid for any aperture-type antenna, but the efficiency factor must reflect the actual antenna type being analysed.