Ultra-wideband (UWB) Echo Synthesis Using Frequency Diverse MIMO Sonar

The ultra-wideband (UWB) signal can improve the range resolution of an imaging sonar greatly. However, the imaging sonar can hardly emit the UWB pulse due to the limitation on the instantaneous system bandwidth. In this paper, by using the frequency diverse multiple-input multiple-output (FD-MIMO) sonar, we propose a UWB echo synthesis method as an alternative. We use a group of FD linear frequency modulation (FD-LFM) pulses with relatively small bandwidths as transmitting waveforms. To suppress the cross-correlation function (CCF) interferences, we use the multi-ping illumination to enlarge the frequency band gap between the FD-LFM pulses emitted in a ping. Moreover, the amplitude errors and the phase errors in a ping (out of the transmission synchronization errors on the transmitting array of the MIMO sonar) and between different pings (caused by the range misalignment due to the multi-ping illumination) are considered, and the corresponding impacts on the synthesized UWB result are analyzed. Numerical simulations show that the proposed method can synthesize a high-resolution range profile similar to that produced by a single UWB pulse, by using a small instantaneous system bandwidth.