Antenna Beamwidth
Estimate the half-power (−3 dB) beamwidth of a parabolic antenna, θ = 70·λ ÷ D, from the wavelength λ (from λ = 0.3/f, with f in GHz) and the reflector diameter D (m). The result, in degrees, is the angle within which the antenna concentrates most of its energy: larger dishes and higher frequencies produce narrower beams and thus more directive, higher-gain antennas, but with more critical pointing. The ~70 factor applies to typical parabolic reflectors. Enter the reflector diameter and the frequency.
Resultado
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Largura de feixe de antena
O ganho de uma antena diretiva e a largura do seu feixe são duas faces da mesma moeda: concentrar a energia num ângulo menor (feixe estreito) é exatamente o que produz ganho alto. A largura de feixe de meia potência (−3 dB) de uma antena parabólica — o ângulo entre os dois pontos onde a potência cai à metade do máximo — é estimada por θ ≈ 70·λ ÷ D, com λ o comprimento de onda (de λ = 0,3/f, f em GHz) e D o diâmetro do refletor (m), resultando em graus. A relação mostra o mesmo princípio do ganho: pratos maiores e frequências mais altas (λ menor) geram feixes mais estreitos. Um prato de 1 m a 10 GHz tem feixe de cerca de 2°; um de satélite geoestacionário pode ter frações de grau. Essa diretividade extrema é uma faca de dois gumes: maximiza o ganho e rejeita interferências de outras direções, mas exige apontamento preciso — alguns décimos de grau de desalinhamento já degradam o sinal, por isso antenas de feixe muito estreito precisam de suportes rígidos e, às vezes, rastreamento ativo. O fator ~70 é típico de refletores parabólicos com iluminação usual (varia de ~58 a ~70 conforme a distribuição de iluminação da abertura). Informe o diâmetro do refletor e a frequência.
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Calculate the gain of a parabolic antenna, G = 10·log₁₀(η·(π·D ÷ λ)²), from the aperture efficiency η (typically 0.5–0.7), the reflector diameter D (m) and the wavelength λ (from λ = 0.3/f, with f in GHz). The result, in dBi, shows the gain grows with the square of diameter and frequency: larger dishes and higher frequencies concentrate energy into narrower, more directive beams. It is the fundamental calculation in designing microwave, radar and satellite communication antennas. Enter the efficiency, the diameter and the frequency.
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