The relationship between tapped delay-line and FFT processing in adaptive arrays

The use of fast Fourier transform (FFT) processing behind the elements in adaptive arrays is often considered as a means of improving the nulling bandwidth of such arrays. However, it is shown that the output signal-to-interference-plus-noise ratio obtained from an adaptive array with FFTs behind the elements is identical to that of an equivalent adaptive array with tapped delay-line processing. The equivalent tapped delay-line array has the same number of taps in each delay line as the number of time samples in the FFTs, and has a delay between taps equal to the delay between samples in the FFTs. Thus, while the bandwidth performance of an adaptive array can be improved by using time-delayed samples of each element signal, no further improvement results from taking FFTs of these sampled signals. The same bandwidth performance is obtained by simply weighting and combining the time-domain samples directly