Recently, adaptive array beamforming has been applied to medical ultrasound imaging and achieved promising performance improvement. However, the current robust Capon beamformer with spatial smoothing (RCB-SS) is implemented in the time domain, which does not fully utilise the large bandwidth of ultrasound signals and spatial smoothing reduces the effective aperture. In this dissertation, we propose a robust Capon beamformer with frequency smoothing (RCB-FS) and compare its performance with RCB-SS. To further reduce the speckle noise and
utilise the large bandwidth of the signal, we combine RCB-FS and frequency com- pounding (FC) and propose a robust Capon beamformer with frequency smoothing combined with frequency compounding (RCB-FS-FC). The proposed RCB-FS method shows a narrower mainlobe width, lower sidelobes, better reconstruction at higher depths and less speckle than RCB-SS. FC is an e ective method to improve the contrast resolution and suppress speckle noise by combining sub-band images, at the expense of resolution. Compared to standard FC, the proposed RCB-FS-FC method has a better contrast resolution and speckle reduction and a significant improvement in resolution. RCB-FS offers a promising approach to find the optimal weights for the transducers in forming the sub-band images needed for frequency compounding