级联噪声系数计算器
计算多级放大器的级联噪声系数。
Gain
41.0 dBi
Gain vs Dish Diameter
公式
## How Parabolic Antenna Gain is Calculated Antenna gain measures how effectively the dish concentrates energy compared to an isotropic radiator. ### Formula **G = eta x (pi x D / lambda)^2** **G(dBi) = 10 x log10(G)** Where D is diameter, lambda is wavelength (c/f), and eta is aperture efficiency (typically 0.5 to 0.7). The beamwidth approximation is **theta = 70 x lambda / D** degrees.
计算示例
A 1.2 m dish at 12 GHz with 55% efficiency.
- 01Wavelength: 0.3 / 12 = 0.025 m
- 02pi x D / lambda = 3.1416 x 1.2 / 0.025 = 150.8
- 03G linear = 0.55 x 150.8^2 = 0.55 x 22,741 = 12,508
- 04G dBi = 10 x log10(12508) = 40.97 dBi
- 05Beamwidth: 70 x 0.025 / 1.2 = 1.46 degrees
常见问题
What is aperture efficiency?
It accounts for feed illumination, spillover, surface accuracy, and blockage. Typical values range from 50-70% for standard dishes.
Does higher frequency always mean more gain?
For a fixed dish size, yes. Higher frequency means shorter wavelength, so the dish captures more wavelengths across its aperture.
What is dBi?
Decibels relative to an isotropic (omnidirectional) antenna. A gain of 40 dBi means 10,000 times more focused than omnidirectional.
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