I've been away from Yagis for many years. But, maximum gain requires
maximum radiation which requires maximum current which requires lowest
radiation resistance. Twenty years ago, or so, Ro of 15 to 20 ohms was
common in high gain Yagis wher Gamma matching was used to raise the
impedance to approximately 50 ohms. A slight reduction in gain allows Ro
of close to 50 ohms.

Kraus, Antennas, McGraw-Hill 1950, Chapter 11 provides the analysis for
a simple 2 element 'Yagi' type array. In written terms, the driving
point, feed point, resistance, ignoring losses, is the radiation
resistance of the driven element minus the ratio of the mutual impedance
to the self impedance of the parasitic elements. Far field gain is
maximized by a term where the input power is divided by the net
impedance of the driven element minus the net impedance contributed by
the parasitic elements.

Conclusion, maximum gain, in any configuration [3 element, 4 element,
etc.], requires lowest Rr produced by highest mutual coupling.

I'm not arguing that more gain is produced by the longest boom or the
most elements. What I am stating is that for any configuration the gain
for that configuration is MAXIMIZED when the Rr is minimized.



Ian White, G3SEK wrote:
Dave Shrader wrote:

If the Yagi is to be tuned for MAXIMUM gain, and that is the
objective, then Ro will be the lowest value at resonance.


That's an interesting assertion. Do you have further evidence for it?