I thought that when combining 2 antennas the spacing between the antennas as well as the lengths of the attached feed lines (phasing harness) was frequency/wavelength dependent and relatively narrow. I don't understand how this can be done over such a wide frequency range like the whole UHF air band. Seems the combination would be optimum at one frequency but cancel out at a multiple, i.e when spacing goes from say 1/4 to 1/2 wavelength. 2 antennas combined over a 225-400 Mhz range would have that issue I think unless there's more to this antenna than meets the eye. I asked the seller but they weren't much help. Let me know if you get 'er in the air!
The antenna he saw is used by a European military entity and is mil-grade. The spacing rule doe not apply in this case as the antenna is designed for near horizon signals that will arrive at the two antennas in phase. After that, if feed lengths are the same and the impedance is taken care of, there will be no problem. the standard reference on this is Kandoian et. al. in Electrical Communication, June, 1948. but 3dB gain is not much for the effort and probably why it is not common.I agree and at one particular frequency you could have 3dB of gain but that should diminish when you get far enough away from the sweet spot of the stacking height and feedline length. If it was a successful design I think you would see more of them and from various companies.
I am not sure I will ever set it up--sort of a splurge buy that ended up in my shed after I realized how big it was. Like I mentioned, 3 dB is not much and I know I will not use it to replace the discone at the top of my tower so I am not sure I will ever get a meaningful comparison.Thanks guys. Makes sense. It does seem ungainly compared to the sleek "stacked dipoles in a radome" approach. Still would like to hear how it performs if you get yours operational dlwtrunked .