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

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.

Re-thinking on the results, the gain difference is probably due to the fact that
the ARRL Antenna Book graph gives dBd, whilst EZ-NEC gives dBi.

But what about the great difference in front-to-back?

Tony I0JX

Antonio Vernucci wrote:
But what about the great difference in front-to-back?

A later edition of The ARRL Antenna Book shows that
equal bilateral gain occurs at a little over 0.1WL
spacing. EZNEC agrees.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Thanks that's right.
73

Tony I0JX

"Cecil Moore" ha scritto nel messaggio
...
Antonio Vernucci wrote:
But what about the great difference in front-to-back?

A later edition of The ARRL Antenna Book shows that
equal bilateral gain occurs at a little over 0.1WL
spacing. EZNEC agrees.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com