An apparatus (10) for providing ultrasonic energy for deposition in body tissue (24) including an array (17) of elements (18, 20) having at least two different sizes and at least one element being periodically spaced with respect to the other elements in the array. An amplifier system (12) includes amplifiers (15), and phase shifters (16) each individually controlling each of the elements producing a beam of ultrasonic energy having reduced grating lobes. Reduced grating lobe magnitude permits improved ultrasonic beam focusing and/or the use of larger element sizes.
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