Parabolic Antenna Gain
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.
Resultado
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Ganho de antena parabólica
Uma antena parabólica funciona como um espelho que concentra as ondas de rádio incidentes (paralelas) num único foco — ou, na transmissão, transforma a emissão de um alimentador no foco num feixe estreito e paralelo. Quanto maior o prato e maior a frequência, mais apertado é o feixe e maior o ganho: G = 10·log₁₀(η·(π·D ÷ λ)²), com η a eficiência de abertura (quanto da área do prato é efetivamente aproveitada — tipicamente 0,5 a 0,7, limitada por perdas de iluminação, bloqueio do alimentador e imperfeições da superfície), D o diâmetro (m), e λ o comprimento de onda (m), obtido de λ = 0,3/f com f em GHz. O resultado vem em dBi (ganho relativo a uma antena isotrópica). O ponto central é que o ganho cresce com o quadrado de D e de f: dobrar o diâmetro do prato (ou a frequência) quadruplica o ganho linear (+6 dB). É por isso que antenas de satélite, radar e enlaces de micro-ondas usam pratos grandes e frequências altas para alcançar ganhos de 30, 40, 50 dBi — concentrando toda a potência num feixe lápis. O preço é o apontamento crítico: feixes muito estreitos exigem alinhamento preciso. Informe a eficiência, o diâmetro e a frequência.
Related Tools
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.
Fresnel Zone Radius
Calculate the first Fresnel zone radius, r = 17.31·√(d₁·d₂ ÷ (f·(d₁+d₂))), from the distances of each end to the point d₁ and d₂ (km) and the frequency f (GHz). The result, in metres, defines the ellipsoid around the line of sight that must stay clear of obstacles for a radio link to work without diffraction loss. Rule of thumb: at least 60% of the first Fresnel zone should be unobstructed. It is essential in designing point-to-point, microwave and long-range Wi-Fi links. Enter the distances and the frequency.
EIRP (Effective Radiated Power)
Calculate the equivalent isotropically radiated power (EIRP), EIRP = P_tx + G − L, adding the transmitter power P_tx (dBm) to the antenna gain G (dBi) and subtracting cable and connector losses L (dB). The result, in dBm, is the power a theoretical isotropic antenna would need to radiate to produce the same power density in the direction of the real antenna's maximum gain. It is the quantity regulated by telecom authorities (legal EIRP limits) and the transmit-side starting point of a link budget. Enter the transmitter power, the antenna gain and the losses.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.