A 7el “owa” yagi on a 12,09 Meter boom, using “maco” style element diameters.:

 

11,74 dBI freespace gain and a 32,03 dB front to back (23,67 front to rear)

  At 18 meter height the antenna produces 17,19 dBi under a 8 degree take off angle.

 

Element (half element) Length

Distance                             Length
0                Reflector       2 x 2,81 meter
1,496 M     Radiator        2 x 2,72 meter
2,122 M     Director 1     2x 2,555 meter
3,596 M     Director 2     2x 2,497 meter
5,816 M     Director 3     2x 2,490 meter
9,000 M     Director 4     2x 2,466 meter
12,086 M   Director 5     2x 2,386 meter

Dont forget “maco” elements are used.

If you need other diameters, please use the forum.