A method for operating a health parameter monitoring system is disclosed. The method involves transmitting radio waves below the skin surface of a person, receiving radio waves on a two-dimensional array of receive antennas of an antenna array, the received radio waves including a reflected portion of the transmitted radio waves, determining an alignment of the antenna array relative to a vein in the person in response to the received radio waves, and outputting a signal that is indicative of the determined alignment of the antenna array relative to the vein.
