tom wrote:
Note that none of these are particularly close to resonance at the
design frequency.

Yagis do have a resonant frequency but that frequency
is not at the design frequency. At the resonant frequency,
the forward gain and F/B ratio are not optimum. At the
optimum forward gain frequency and/or F/B ratio frequency,
the Yagi, sans matching network, is not resonant.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com