Dynamic Beam Forming using Chirp Signals (BeBeC-2018-D4)

Beam forming generally gives good lateral spatial resolution control but poorer axial resolution. For active array systems, in which echoes are received from a transmitted pulse, swept frequency chirp pulses give very good axial spatial resolution. This is because the phase of the echo from a particular range needs to very accurately match the phase of the reference transmitted signal with which it is compared in the matched filter. The result is an axial resolution inversely proportional to the swept frequency bandwidth, and independent of the pulse duration. We describe how this tight phase requirement also gives tight lateral resolution for a chirped pulse, because decorrelation in the matched filter occurs rapidly off-axis. This gives scope for dynamic beam forming for active arrays based on the pulse design, or on what part of a swept frequency pulse is included in the matched filter.