What does a complex matched filter mean? . A complex bandpass filter can be formed by multiplying a low pass filter by exp(jwt) getting an analytic filter (one sided in the frequency domain) which is complex, the filter will have complex coefficients but it is implemented as two filters with real coefficients (coefficients multiplied by cosines for the real and the same coefficients multiplied bu sines for the imaginary) but how about the matched filter which is supposed to be a low pass filter centered around DC? how does that one look like?