Co-phasing or “stacking” has long been a way to get high gain from antennas. Co-phasing involves placing two (or more!) identical antennas either side-by-side or one over top another (“stacking”) at a certain distance apart (usually a 1/2 Wavelength or more) and feeding the antennas in-phase. The result is 3 db more than just a single antenna. In my opinion, this is the absolute way to go with beam antennas instead of going with say, 8 elements beams, it would be much better to go with co-phasing two 4 element beams. If you look at the gain figures for a 8 element beam, you see that you will end up with more gain if you co-phasing 4 elements instead. If you are considering co-phasing antennas for your mobile, better check out the “Mobile” section first.