To generate information representing a volume, co-arrays or synthetic transmit aperture process is performed in one dimension and beamforming is performed in another dimension. For example, a transmit aperture focuses in azimuth, but is unfocused or divergent in elevation. A multi-dimensional array receives reflected echoes. The echoes are beamformed for sub-arrays for focus in azimuth. The resulting partial beamformed information is provided to an imaging system from the probe housing for completion of beamforming at least in elevation.