I have a need to have a *very flat* passband for some of the analysis I'm doing of neutral hydrogen. Real hardware, of course, produces passbands that aren't quite flat--some worse than others. So, I've tried an experiment in one of my flow-graphs where I take the (aggressively-averaged) FFT magnitudes by taking each bin magnitude and dividing by the maximum, and then using the inverse of that to produce a correction curve, as normalized magnitudes. I then use those normalized magnitudes in an FFT filter (after converting into time-domain), and the result works less-well than I would expect. The result is a *much-flatter* spectrum, but at the fine-scales I'm doing analysis at (0.5dB), it's not nearly as flat -- the outer edges are under-corrected, and the inner bits are over-corrected. Anybody have any pointers to good papers on passband flattening techniques?
on 2013-04-08 20:12