The BatBeam Project

Make the antenna change its shape between RX and TX.  Max pattern for RX max gain for TX.  This therefore would not be a freq agile antenna but a pattern agile antenna 

73  W9OY

The incidence of highest forward gain generally does not coincide with the incidence of best receiving pattern with deep F/B and F/S.  So by changing element length dynamically with TX v RX, you can design in more gain on TX which is desirable and best pattern on RX which is desireable.  On RX gain is not most relevant since it is signal to noise that dominates, and the whole point of a beam on RX is to eliminate unwanted noise.  On RX you basically always have more gain in the signal chain than you can use.  So changing the shape of the antenna on TX v RX maximizes each goal within a single antenna.  This idea is no different than using a 4 square on transmit (max directional gain) but using a beverage (max directional signal to noise) on receive on say 160M.   

73  W9OY