1. An ultrasonic diagnostic scanhead comprising: a scanhead enclosure; an array of transducer elements extending in at least two dimensions, located in the scanhead enclosure, and exhibiting a plurality of groupings (patches) of localized elements; a plurality of microbeamformers, located in the scanhead enclosure and coupled to the patches, each of which acts to beamform the signals received by the elements of a patch, each microbeamformer applying delays to a receive echo sequence which are adjustably advanced or retarded as the echo sequence is received, whereby at least one of the steering and focusing of the beam formed from the echo signals received by the elements of the patch is varied as the echo sequence is received.