An ultrasonic diagnostic imaging system transmits a plurality of focused beams normal to the plane of a transducer aperture and receives multiple receive lines in response to each transmitted beam. Sub-apertures of the transducer aperture are defined by apodization and signals of the sub-apertures are aligned and combined to produce signals exhibiting the effect of transmit steering at different angles with respect to the sub-apertures. The steered signals are detected and the detected signals relating to common points in an image field are combined. The combined detected signals are used to produce an ultrasound image with reduced speckle.