Filtering technology
J. Lillington · Communications Engineer · 2003
The author presents an in-depth look at the key differences between the responses of FFT and polyphase DFT filter banks. The subject of filter bank frequency response is a complex one. Although most texts on the subject deal with the steady-state response, in the real world, radar and other burst-mode signals are very transient in nature. It is, therefore, important to understand the transient performance of filter banks. In general, the better the frequency discrimination properties, the longer the time taken to settle. This is because sharper filters need more taps and have longer impulse responses. Consequently, during the settling period, the filter taps are not filled and the frequency response to adjacent channels can actually be worse than that of the unweighted FFT filter bank. The author makes comparisons between FFT and polyphase DFT filter banks and looks at both the steady state and the transient conditions.