Let's say we want to estimate the amplitude A of a mono-frequent signal using a windowed DFT. The frequency of the signal is unknown, and the frequency resolution of the DFT is limited, thus it cannot be expected that there is a DFT bin that matches this frequency directly. Therefore, A is estimated from the amplitude of the next closest DFT bin. Now the question is,
should the frequency response of the window exhibit a narrow or a wide mainlobe to obtain a good estimate, and why?