For radio direction finding it is a lot easer to use the difference between two signals.
You could for example put two receivers on your copter and detect the difference between the two but you would be adding weight to the copter.
A better option would be to use two signals on the ground and let the copter detect the difference of the two signals. But even two signals will not work. To land the copter you need both X and Y with a hint of Z.
On the ground, take two omni antennas and put a vertical medal plate between the two antennas. When you are edge on to the plate the two signals will be equal strength. As you move from this, one will get stronger while the second gets weaker.
To be able to land you need at least three antennas. To home, the copter just flies to increase the signal it can hear. At some point the copter will start receiving a second signal. The flight path changes so that this signal is also increasing. Again at some point the copter will start receiving the third signal. The copter just keeps going until all three signals are the same strength at which point the copter starts descending while keeping the signals the same strength.
So your landing platform is setting on three medal plates with 120 degree difference between the plates.
A small gap between the three plates center would allow some of the signal of the shielded transmitter to leak through the gap. This could be used as a getting close to over the center. The size of the shields especially the hight aspect will make this work better.
You do not have to transmit from all three antenna's at the same time just rotate through the three antennas. This actually makes it easer to process on the copter.
Remember for this you need to allow time for the copter end to adjust to the different signals if you are just using it's receive strength level for this.
http://en.wikipedia.org/wiki/Corner_reflectorFor 3 antennas you want a 120 degree corner. If you decide that 4 antennas is easer then 90 degree corner.
Note that even if you have very good corner reflector antennas, at a close distance there will be some signal off the side. If this is still to strong a signal to center the copter on the platform then some space between the reflectors and more hight could help.
C