STACKING VERTICALLY SPACED YAGI ANTENNAS, A KNOWN BUT NOT USED APROACH (Part I)

It is a common practice these days using vertically stacked directional antennas, in particular yagi - udo type. The effect of vertical stacking was very well described by James Lawson W2PV in his historical \"Yagi antenna design\" book. 

http://dxnews.com/ua9ba-stacking-yagi-part-1/