quadrifilar helical antenna

I'm trying to decide on the axial length and diameter of a 1/2 turn, lamda/2 quadrifilar helical antenna. I've read that one good geometry is 0.27*lamda in height (or axial length) and 0.18*lamda in diameter. So I'm wondering, when people call it the lamda/2 quad, does the lamda/2 refer to the axial length x2, since the total length of one of the bifilar loops is lamda/2? Or are quadrifilar helices generally lamda/2 long, but when you reduce the diameter to 0.18*lamda, the axial length is really reduced by that much (to 0.27*lamda). Basically, what's better, ~lamda/2 or ~lamda/4 axial length?

Thanks!

Or are 0.5*lamda lengths used, except this is the electrical length of the helix and not the axial length? No papers have a good diagram and explicitly explain which lengths they refer to.

Hi,
This kind of QHA is resonant type and its electrical length(l) is equal Landa/2.
l^2=p^2+(2*pi*R)^2
(p=pitch length)
you can find more information in "Kilgus" 's articles.
Good luck