Yagi-Uda antenna design parameters

These were published in 1968 based on experimental results. I don't totally get them. Shouldn't R be slightly larger than .5 if the drive element F is .5?

d is the diameter of the elements
Optimal Lengths for Yagi-Uda Elements, for Distinct Boom Lengths
Boom Length of Yagi-Uda Array, in λ
0.4 0.8 1.2 2.2 3.2 4.2
D2 0.4240.4200.4150.4200.424
D3 0.4280.4200.4070.4070.420
D4 0.4280.3980.3980.407
D5 0.3900.3940.403
D6 0.3900.3900.398
D7 0.3900.3860.394
D8 0.3900.3860.390
D9 0.3980.3860.390
D10 0.4070.3860.390
D11 0.3860.390
D12 0.3860.390
D13 0.3860.390
D14 0.386
D15 0.386

Spacing between directors, (SD/λ)
Gain (dB)9.2511.3512.3514.4015.5516.35
The ACTUAL likely source for the above table might be the The NBS Yagi Report. It appears that the reflector is short because they used a folded dipole (loop) instead of a half-wave dipole. dang. Still scouring this report for dimensions of the folded dipole (loop)

Folded dipole

Impedance of a typical dipole is around 70 ohms, close to 75 typical for coax feed. The folded dipole Z ir roughly 4* as high, 280 ohms, which is close to the 300 ohms for typical for twin-lead transmissions lines.

Folded dipoles, center driven, resonate at 0.5λ, 1.5λ,...
driven from the side, they resonate at integer multiples of λ

Rough guide for typical 1/2 wave dipole resonator:
Aaron Birenboim
Last modified: Tue Oct 9 05:51:19 MDT 2012