The Cantenna can not be have 12 dBi gain. Any Cantenna design, I have
testet, had only a performance from 7 to 8.5 dBi.
I found some Canntenna models (.NEC-files) on internet, which
calculates indeed 12 dBi. But the average gain test, which is almost
not done, shows the error in the design model.
If you check and correct this desing errors, you will get only a
performance of 8 dBi.

It is not true, which the cantenna has 12 dBi! Keep in mind.
Aziz