A 2D array transducer (10) is separated into a plurality of sub-arrays. Four representative sub-arrays from SA1 to SA4 are shown in an enlarged manner. In addition and the 2D array transducer (10) is segmented into a plurality of transducer regions. Four regions of (i) - (iv) segmented by dot-and-chain lines represent four transducer regions. For each sub-array and a delay process corresponding to the sub-array is executed based ON a delay pattern defining an amount of delay for each of the plurality of transducer elements belonging to the sub-array. In this process, for each transducer region and a common delay pattern is set for the plurality of sub-arrays belonging to the transducer region. For example and because sub-arrays SA1 and SA2 belong to the same transducer region (iv), a common delay pattern is set for the sub-arrays SA1 and SA2.
