An ultrasonic diagnostic imaging system has a two dimensional array arranged in multiple patches of multiple transducer elements. Each patch of transducer elements is coupled to a group of microbeamformer delay lines having outputs coupled to a channel of a system beamformer, which beamforms the partially summed beams of each patch into a final beamformed signal. The outputs from multiple patches which are not simultaneously used in the active receive aperture are coupled to a common beamformer channel, enabling the number of patches of the array to exceed the number of channels of the system beamformer without the use of multiplexers.