Tal Dayan wrote:
> I presume that you are looking for an active sonar (both TX and RX) so one
> thing you need to decide is are you going to form the phase array for both
> TX and RX or only for RX. The RX side is easier since it does not involved
> power and you can do everything with DSP. For example, some sonar systems
> have at the very front an analog multiplexer that sample the hydrophones
> signals (after the preamps) in a very high rate. This is then fed to a
> digital processing unit that does the beam forming in all directions at the
> same time using a single arithmetic unit. This way you don't need to have to
> rotate the transducer array.

I'm planning to do all of the beam forming digitally as well. You mentioned an
analog multiplexer. I had assumed that all of the ADC samples need to be taken
simultaneously. How necessary is that?

> The beam forming itself is pretty simple, you take a bunch of hydrophone
> signals, delay them proportionally to match the additional wave path in the
> desired direction and then some them using predefined weights. The delay is
> set such that when a signal arrives from the center direction of the beam,
> the signal after the delays have 100% correlation. If you have the geometry
> of the array it is pretty easy to calculate the gain of the bean in various
> directions.

I understand the beamforming principles right up to the part about predefined
weights. How do I determine the weights? I've also seen mention of "null" beams.
What are they?

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