For a three-element Yagi antenna, what approximate element spacing (in wavelengths) provides the best compromise between gain and front-to-back ratio?

In Yagi antenna design, the spacing between elements significantly affects both forward gain and the front-to-back ratio. Extensive modeling and practical testing have shown that spacing elements at approximately 0.20 wavelengths yields the optimal balance between maximizing forward gain and minimizing rearward signal pickup. A spacing of 0.50 or 0.75 wavelengths is much too wide for standard Yagi parasitic coupling. Conversely, 0.10 wavelengths is too close, which would increase element interaction excessively, drastically lowering the feedpoint impedance and shrinking the bandwidth.