Elevation beamforming performance of a 1.75 D array

1.75 D arrays allow limited beam steering in elevation, which is valuable for three-dimensional (3-D) imaging within a certain field of view. 3-D imaging has important advantage in detecting and visualizing small lesions from multiple viewing angles. Recently, Tetrad Inc has manufactured 1.75 D arrays using the state-of-the-art technologies. The array we have consists of 10 rows in elevation and 128 elements in azimuth, 1280 elements in total. The central frequency of the array is 5 MHz and the bandwidth is 60%. We have constructed 1280 parallel transmission circuitry, 1280 to 40 multiplexing and 40 parallel receiving circuitry. Upon each transmission, 1280-element RF signals were multiplexed to 40 parallel electronic channels, amplified, sampled and stored in the PC. The elevation performance of the array was evaluated through simulations and experiments using a point target. The parameters evaluated were -6 dB, -20 dB beamwidths and grating lobe strength.