Increasing folded dipole element diameter has the following effects:

1) Antenna bandwidth increases (the VSWR changes less with frequency changes). However, the bandwidth of a folded dipole already is significantly wider than the bandwidth of an unfolded dipole, so the percentage of bandwidth increase is less than the percentage increase would be if an unfolded dipole diameter was increased the same amount.

2) Yagi antenna forward gain at resonance decreases slightly. The amount of gain reduction depends on the number of parasitic elements and whether their diameters also are increased. With no parasitic elements the gain reduction is minuscule. The gain reduction is greater with an increasing number of elements and if their diameters are also increased.

There is no difference in antenna RF performance between solid and tubular antenna elements at such a high frequency, because nearly all the RF current flows very near the surfaces of the conductors.

The radius of the bends at the ends of a folded dipole has very little effect on antenna performance with the relatively narrow spacings normally used between folded dipole elements. However, if the spacing between dipole elements is an appreciable fraction of a wavelength a radiator will have the characteristics of a loop antenna, rather than a dipole. Loop antenna characteristics cannot be summarized simply without specifying all the dimensions.