The rectangular window has a value of one over its length. The following equation defines the rectangular window.
w(n) = 1.0 for n = 0, 1, 2, …, N - 1
where N is the length of the window and w is the window value.
Applying a rectangular window is equivalent to not using any window because the rectangular function just truncates the signal to within a finite time interval. The rectangular window has the highest amount of spectral leakage.
The following figure shows the rectangular window for N = 32.
The rectangular window is useful for analyzing transients that have a duration shorter than that of the window. Transients are signals that exist only for a short time duration. The rectangular window also is used in order tracking, where the effective sampling rate is proportional to the speed of the shaft in rotating machines. In order tracking, the rectangular window detects the main mode of vibration of the machine and its harmonics.