In ac6la's website, I found a simple program to generate a moxon antenna model.
This program also exports the calculated dimension into a .nec file, very useful for our 4nec2 simulations.
Here is the moxon antenna's features:
Not bad, isn't it? Being a very little and simple to homebrew antenna, it gives its 6 dB in a 140 degrees (@ -3 dB) and, that's more interesting, a wonderful front to back ratio (near -44 dB), very nice when playing at fox hunt ;-).
It is not worth trying to optimize this very good antenna, so here is the antenna Moxon's .nec file, directly from MoxGen program.