[Antennas] Quad Design Question

[Raymond W Brann]

Greetings Again, Can anyone supply me with a formula for the Directors
on a Cubical Quad antenna, and tell me the source of your info.

I'm writing a computer program very similar to the online Quad "java" 
calculators
and would really appreciate the info.
Oh, I do have a formula for the 1st Director 975 / F (MHz)
but no real info about maybe .........2 thru 5

I also realize that any formular would be dependant on a multiple of
factors ......just need a starting point.

Many Thanks
Ray / W1RWB