Antenna Theory One: Stacking and Baying Antenna's
Contrary to popular belief stacking and baying is not hard, I have had over the couple of years I've been licenced a number of licensees ask me how its done, ranging from Full licensees (when I was an M3 Foundation holder) to new trainees.
Most commonly you will find Udo-Yagi's stacked and bayed for contesting, EME and Meteor Scatter. You can also bay and stack other antenna's such as Quagis and cubic quads, plus many other designs.
What are the Benefits of Stacking and Baying?
Stacking: Placing one Antenna above the other, usually in multiples of Two
Baying: Placing one Antenna next two the other usually in mulitples of Two
Stacking and Baying: Creating a square of antenna's like this fine example 
A fine example by AF9Y
Simple stacking allows the gain from a single antenna to be increased, this is useful for range work but decreases the beam height. Likewise baying increases the range but decreases the width of the beam. Thus an array with stacked and bayed antennas will be narrower on both the horizontal and vertical yet have an increased gain.
Antennas are usually stacked and/or bayed, or both in multiples of 2 antenna's although sometimes 3 and 5 may be used, but this causes issues with creating the feed looms.
How Do I stack Antenna's?
Firstly each antenna has an area of effect (in this case an oval
). What we are aiming at doing is putting the antennas one above the other whilst keeping the oval area of effect just slightly apart. If they overlap then the stacking will not work. Stacking the antenna's is only the first part. Then what we need to do is create the wiring loom to wire the Stack. This is often seen as the hard part, which is not exactly true. What we will do is assume that we are working with two stacked antennas
- You need to measure the distance between the antenna's and add say 6cm's on.
- Divide this figure by two and cut two lengths of feeder to the length you have measured then attatch one end of each feeder to each antenna.
- This leaves you with two ends of feeder, put SO239 on each of the feeders.
- You will then need a T connector, then all you need to add is a feeder. Remember keep your lengths beyond the feeder the same and you won't go wrong.
What if you want to Stack 4 Yagis? You repeat Stages one through 4 twice, keeping all the feeder lengths equal, then you measure the distance between your two SO239 T peices, cut a length of feeder again 6cm too long, then put a SO239 on the end of all four ends, connect one end of each to the T peices already wired, then connect the other two ends to another T peice, then like above all you need is your feeder.
Remember that your lengths between antenna and T peice have to be equal for EVERY Antenna! otherwise you will have problems.
How Do I Bay Antenna's?
Baying is exactly the same as Stacking as far as the theory goes, and from the information you have above, you should be able to build a bayed system with ease. Just remember that the manufacturer of your antenna will usually give you the stacking and baying distances. Looms for wiring are exactly the same and should be exactly the same lenghts for all antenna's.
Notes.
If you are stacking and baying antennas I'd be tempted to give yourself more than the 3cm leaway that I've quoted above, I personnally use 10cm
Why not try stacking or baying or both Hentennas or unusual antennas for contests, it will make for interesting topics of discussion at local clubs and possibly magazines.