Subaperture decoding to enhance performance of coded excitation

Coded excitation requires long code to improve signal to noise ration (SNR). However, in order to achieve a high lateral resolution, the beam forming is normally performed based on a low f-number and realtime dynamic focusing, which limits the maximum length of coded waves. Individual decoding before beamforming can solve this problem, but it demands an enormous size of hardware. In this study, a subaperture decoding technique is proposed to achieve a high SNR based on coded excitation without compromising lateral resolution. In this technique, the receiving aperture is divided into N subapertures, beamforming is performed for each subaperture, and each output is decoded, delayed and summed together to complete beamforming in whole aperture. Computer simulations were used to demonstrate this technique. When the transmission waveform was encoded by the 13-chip Barker code and decoded with a mismatched filter, and the reception f-number was 1, the proposed technique, with the number of subaperture of 16, lowered the range sidelobe level from -25 dB to -45 dB.