The solid line is gain as obtained directly from NEC2, calculated from the absolute value of the far field in the forward direction. The dotted line is the gain as calculated from the far field in the forward direction divided by the average far field. The dotted line includes ohmic losses. Feed point impedance vs number of segments per element. Original NEC2 for a 9 element yagi with 9mm elements on 144 MHz.
Solid line is real part and dotted line is imaginary part.
The results produced by NEC2 depend too much on the segment length for NEC2 to be a really nice model to optimise yagis in. With the modified version of NEC, the calculation results are much less depending on the number of segments. See the diagrams below or the numerical data. Gain vs number of segments per element. Modified NEC2 for a 9 element yagi with 9mm elements on 144 MHz.