Generally speaking, the narrower the main lobe beam width of an antenna, the higher the antenna gain.

　　1) For general antennas, when the sidelobe level and front to back ratio are normal, the following approximate calculation formula can be used:

　　G(dBi)= 10Lg { 32000 /( 2θ3dB,E ×2θ3dB,H )}

　　In the formula, 2 θ 3dB, E and 2 θ 3dB, H respectively represent the lobe widths of the antenna on the two main planes;

　　32000 is the empirical data obtained from statistics.

　　2) For upright omnidirectional antennas, there is an approximate calculation formula

　　G(dBi)= 10Lg { 2 L / λ0 }

　　In the formula, L is the length of the antenna; λ 0 is the central working wavelength;

　　3) For parabolic antennas, there are

　　G(dBi)= 10Lg { 4.5 ×( D / λ0 )2 }

　　In the formula, D is the diameter of the paraboloid; λ 0 is the central working wavelength; 4.5 is the empirical data obtained from statistics.

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