[DonRotolo]

Eric:

Yes, it is absolutely true that adding data to the system will often provide for a more complete solution. However, for this application I'm not convinced that, say, 8 antennas will improve the pointing direction accuracy by even 10 degrees.

Doppler isn't working on signal strength, but the doppler frequency shift caused by the (electronic) rotation of the antennas. In order to have a detectable frequency shift, the antennas need to be "rotated" very quickly. More antennas means more switch 'changes' per second, less time to capture and process the doppler-shifted signal, and the design and performance burdens associated with having to do all this faster and with less signal.

We often use 4 antennas because it is easier to do the math, however 3 would also work, as would 8. Some Doppler units DO use 8, but I have yet to find claims that they point to the transmitter any 'better' than a 4-antenna unit. All that is gained is capture area, which is only useful if the signal is close to the receiver's lower limit (i.e., weak) - and even then, the effect is marginal.

Thus my statement.