In previous parts of this series, we described how, when a wavefront approaches an array of elements, there’s a time delay between elements based on the wavefront angle θ relative to boresight. For a single frequency, the beamsteering can be accomplished by replacing the time delay with a phase shift. This works for narrow-band waveforms, but for wideband waveforms, where the beamsteering is produced by a phase shift, the beam can shift direction as a function of frequency.
Such a situation can be intuitively explained if we remember that a time delay is a linear phase shift vs. frequency. Thus, for a given beam direction, the phase shift required changes as a function of frequency. Or, conversely, for a given phase shift, the beam direction changes as a function of frequency. The concept of the beam angle changing as a function of frequency is called beam squint.