[TowerTalk] Stacking Antennas

[jimlux]

K4SAV wrote:
> YO is not likely to work well for stacking dissimilar antennas.  You 
> might be able to do it with NEC if you are very careful and model the 
> entire system.  If the antennas happen to have dissimilar matching 
> networks, the phase delay thru the matching networks can be very large.  
> For example a transformer match might have near zero phase delay while a 
> hairpin match might have 25 or 30 degrees of delay.
> 
> Jerry, K4SAV


Jerry brings up an interesting point.  A lot of times, one optimizes an 
antenna design ignoring the details of the feed or matching network 
(because it often has no effect on the pattern or "radiation 
performance"). You optimize the element spacing and length, and then 
make a matching network to fit, without a huge amount of concern for the 
phase shift through the network. In a phased array (which is what a 
stack o' Yagis is), the matching network is a big deal.

It could be a bit of a modeling challenge, if the network isn't modeled 
mechanically, but as lumped components, and it has significant coupling 
to the field.  And that whole "conductors close together with corners" 
is one of the trickier things to model with a NEC type code.