Matrix arrays for endoscopic and catheter-based applications are restricted to small physical apertures, which limits their lateral resolution. In addition, when aiming for high volume rate imaging and utilizing the recent methods of transmitting a single or few diverging waves (DW), lateral resolution further deteriorates. In this work, we propose a high frame rate transmission scheme which outperforms alternative methods in lateral resolution. To improve the lateral resolution and side-lobe level, we propose to transmit only on a sub-aperture on either side of the array and apply a specific weighting function to received data. Compared to single-DW imaging, the proposed Sub-aperture Virtually Extended Array reduces the PSF width and sidelobe level by 16% and 5dB respectively and provides a similar SNR at the cost of halving the frame rate.