Theoretical evaluation of a 50 MHz split aperture linear phased array

The development of transducer arrays for high frequency medical imaging is complicated by the extremely small dimensions of the array elements. For example, a 50 MHz linear phased array requires a center to center element spacing of only 15 /spl mu/m. Fabricating an array with these dimensions is difficult using conventional technology. A split aperture design that permits much larger element spacing (3-4 times) while avoiding the formation of grating lobes is described. The 3D radiation pattern of a 2.0/spl times/1.4 mm, 50 MHz split aperture phased array with 32 transmit elements and 32 receive elements was evaluated theoretically. The array was designed using a passive lens in the elevation direction focussed at 7.5 mm and a fixed transmit focal distance in the azimuthal direction focussed at 5.0 mm. Grating lobes in the azimuthal direction were suppressed by 60 dB over the range from 5.0 to 9.0 mm.