Beamforming

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could you please also explain apodization? We are doing beamforming to exagerate the main lobe and aren't the side lobes being supressed by it? or still we need apodization to reduce the side lobe? If yes, please explain in general terms what is it exactly?

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You aren't performing the apodization (windowing) of the receiver responses to exagerate the main lobe, you are applying the apodization to reduce the sidelobes, and that has the side-effect of increasing the main-lobe width. To compensate for this, you can obtain a narrower main-lobe, by adding more receiver elements.

The relationship between the increase in mainlobe width relative to the window function can be calculated using tools like MATLAB. The paper by Harris 1978 has a number of standard windows. It looks like Wikipedia has an explanation as well as a link to the Harris paper:

http://en.wikipedia.org/wiki/window_function

http://web.mit.edu/xiphmont/public/windows.pdf

Cheers,

Dave