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.
学习