Evaluation of the radiation pattern of a split aperture linear phased array for high frequency imaging

Developing transducer arrays for high frequency medical imaging is complicated because of the extremely small size and spacing of the array elements. For example, a 50 MHz linear phased array requires a center-to-center spacing of only 15 /spl mu/m (one-half wavelength in water) to avoid the formation of grating lobes in the radiation pattern of the array. Fabricating an array with these dimensions is difficult using conventional technology. A split aperture design that permits much larger element spacing (3 to 4 times) while avoiding the formation of grating lobes is described. The 3-D radiation pattern of a 1.9/spl times/1.4 mm, 50-MHz split aperture linear phased array with 33 transmit elements and 33 receive elements has been evaluated theoretically. The azimuthal beam width is 90 /spl mu/m at a distance of 4.0 mm. Grating lobes are suppressed by at least 60 dB at distances >4.0 mm (/spl sim/f/2). The elevation beam width is 220 /spl mu/m at 4.0 mm, and a useful depth of field over the axial range from 4 to 10 mm is obtained.