If you have the 21st Edition, you'll find the complete text of the earlier
material on the included CD. It contains more detail about why the
Wilkinson divider isn't appropriate for this application.

Devoldere's _Low Band DXing_ also contains a lot of good information about
phased array feed systems.

Thanks a lot to both of you. I have the two books mentioned above and I did
not suspect the cd rom contained all the former articles published. I did
not use it since the programs on the cd did not install on my pc ;-) About
the Low band dxing, it is very very complicate for a beginner like me and
even if I wrote to the author in order to get more info, he never replied.
So I'm gonna have a deep look at the ARRL cd and also trusting what you
summarized! I've also found a leaflet (published online in pdf ) by HyGain
where they suggest different combinations of phased arrays which use their
verticals and there are no schemes containing the resistor.
I asked since an Italian dxer (i4ewh) in its scheme considers this splitter
absolutely necessary. I spoke with him and he told me the swr was greatly
reduced by this solution. Anyway here is the link so you can have a look.
It's a four element phased array:
http://i4ewh.altervista.org/ShortWav.../Verticali.htm
Once again, I must repeat that low band dxing has no help for beginners and
better and simpler schemes can be found on the simple "vertical antennas" by
arrl and arrl antenna book. If you have any other site or web address where
I can find more material, please tell me.
A last question to both of you: I would like to use this system (centered
for the 20 meters band) also for 40 meters and 10 meters. Should an antenna
tuner suffice?
Francesco ik8vwa