I don't think a tethered balloon would be an ideal platform for such a directional antenna in any vaguely windy location, you need a lot of stability for it to be useful. I'm having difficult imagining any way to make that work which isn't essentially a stayed vertical support with the balloon ... probably not at net helping.
JLENS works with a variety of sensors (optical and RF) today, although I'm more familiar with the smaller systems (just a big tower with a payload on top)
