Medical ultrasound research is typically performed using either video image data, or summed Radio Frequency (RF) data. While such data has led to improved understanding of ultrasound image formation, and in the development of novel image formation and signal processing algorithms, it contains only a fraction of the information available in the individual beamformer channels before summation. This paper describes the development of an advanced experimental system which will simultaneously acquire RF data from 128 individual beamformer channels. We refer to such data, acquired across the transducer face, as aperture domain data. The system will be capable of continuous acquisition over a period of 1.6 seconds, the equivalent of 50 image frames. The system will also incorporate a data interface to allow future connection to custom processing units, ultimately enabling real-time processing of aperture domain data. The system will be constructed around a state of the art Agilent Technologies SONOS 5500 ultrasonic imaging system to enable real-time imaging and preserve broad signal bandwidth, high signal to noise ratio, and high dynamic range. The proposed system will facilitate research on adaptive imaging, system architecture, multidimensional blood flow estimation, broadband transducers, and a number of other areas.