The effect of delay error on the sidelobe level in synthetic aperture imaging

The synthetic aperture method, which synthesizes a large aperture by multiplexing a small transmit/receive aperture, is known to have two major advantages: (1) mainlobe narrower than one-way dynamic focusing in reception, and (2) a hardware volume smaller than in the synthetic focusing method, which requires that every element receives a reflected signal for each transmitting element. This paper describes the influence of delay error on the sidelobe in the synthetic aperture method. The simulation results show that in order to suppress the sidelobe level below -40 dB at 3.5 MHz, the combined delay fluctuations among the small apertures caused by the wavefront distortion in the medium and by the electronics should be less than 3 ns. As the propagation time inhomogeneity in a typical medium such as a phantom test object or a human body causes fluctuations of more than 15 ns of arrival time among the small apertures, the results lead to the conclusion that the synthetic aperture method is not effective on such a medium