A packet header processing engine includes a level 2 header generation unit and a level 3 header generation unit. It includes a pair of frame members each formed by a downwardly convex rocker and an upwardly convex rail joined at front and rear ends. In a preferred form, the transfer device is in the form of a thin piece of flexible material and is moved in the conveying direction from the retracted position to the extended position by engaging with the sweep conveyor and is moved to the retracted position by being wrapped around a rotated roller. The T-R switch architecture is preferably to short-range, single-transducer acoustic ranging systems. First and second portions of the SAR data are accumulated over the first and second partial apertures, respectively, and first and second vector complex image data of the target is derived in response thereto.