I recently noticed I was missing a few pages from my site, one included a great article I wrote on antenna stacking and baying. So I am going to try and reproduce it here
There are two ways to stack antennas one is putting the antennas above each other in a vertical plane known as ‘Stacking’ the other method is known as baying and that is putting the antenna’s side by side on a horizontal plane.
There are many many guides on how to best optimize antennas from DL6WU’s formula’s to what seems to be standard here in the UK of stacking at 1/2λ above the first antenna. What most people seem to forget is you still need to do this calculation even if the antenna’s are on different bands and facing in different directions. What we have to remember is that when we stack or bay we create gain but it costs us in beam width. Just the same as adding another 10 directors would create a lot of gain but an almost needlepoint beamwidth. If you have real estate there is a way round this. Transmitting antennas can be bayed or stacked or even both, and have a separate antenna for receive! of course this creates other complexities. We also have to consider that the F/B ratio of a single antenna has better characteristics as does the back to side ratio a larger antenna will always win out however for many practical reasons larger antennas are not always possible.
I was talking to a fellow amateur in Texas who had an 8×8 array of 5 element antenna’s for 15m can you imagine the size of a beam to match the gain on that? You would be looking at an antenna with many wavelengths in length. All well and good if you happen to be a Rancher, but no good to anyone in a city or town. an 8×8 array in the UK is just not feasible. but a 4×4 array especially on VHF and above is. There must be UK stations using stacked HF antennas but I am unaware of them.
Stacked/Bayed or Stacked and Bayed antenna’s are fed from a splitter which is usually a 1/4λ each antenna is then fed with a quarter wavelength of feeder so the antenna’s are fed in parallel. EXCEPT for BoxKites! Boxkites are fed in a different way and that will be the subject of another page entirely.
stacking will provide you 3 dB, you are likely to read however 2.5 < 2.7 dB is the best real world answer. Connectors, extra lengths of Coax etc all bring down the gain! On top of that we also loose to Sidelobes, the more gain the more issues with Sidelobes appears the question then has to be asked, what really is the benefit of an S Point GAIN! See also Broadside Couplers