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Where is this 1/4 factor coming? I know that for a circular dish, the max resolution is 1.22lambda/(aperture size), so for my scanner it would be (1/4)lambda/(aperture size)

Scanner is 100mm large, so that would do 2/100 radians. Will check up if that matches my simulations.

Thanks for the infos on SAR! Will try doing that!

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>Where is this 1/4 factor coming?

Guesswork... 40khz ultrasound has a wavelength of about 8mm. If your phase from end to end isn't at least 90 degrees, you don't have enough shift to form a beam with. I would imagine if you're clever, and your transducers don't drop off to fast on the sides, and you've got them fairly tightly constrained in X,Y,Z to a regular grid, you might be able to tweak out more resolution slightly off center, because the return phases will more quickly diverge as this angle increases.

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