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. Modified NEC2 for a 9 element yagi with 9mm elements on 144 MHz.
Solid line is real part and dotted line is imaginary part.
Note that, with the modified NEC2, the gain as calculated from the theoretical radiation pattern is constant within 0.005dB from 3 to 39 segments, and that the imaginary part of the feed point impedance is constant. For the purpose of using the model to optimise antennas, this is very valuable. The modified NEC2 will probably allow the design of more critical antennas. From a practical point of view this is unacceptable. With the modified NEC2, a constant correction, equal for all elements should lead to a real world design with a radiation pattern that is very accurately the same as the calculated pattern.