In the 1976 edition of the ARRL Antenna book, at page 147 I see a graph (Fig.
4-37) showing the gain of a two-element array consisting of a driven element and
a self-resonant parasitic element (i.e. same length as driven element, no
de-tuning).

The graph shows gain (in the two orthogonal directions) as a function of
spacing. For spacing = 0.14 wavelength, the graph shows a bi-directional gain of
about 4 dB (and then a front-to-back ratio of 0 dB).

Unless I did something wrong, on EZ-NEC the same array with 0.14 WL spacing
shows a free-space zero-elevation gain of about 6.4 dB in one of the two
directions, with a front-to-back ratio of about 10.5 dB.

Which of the three is wrong: Antenna Book, EZ-NEC or me?

BTW: as far as radiation resistance is concerned, EZ-NEC gives about 17.9 ohm at
resonance, against the nearly 21 ohm shown by the Antenna Book.

Tony I0JX

Rome, Italy