A method for operating a health parameter monitoring system is disclosed. The method involves at a removable smartphone case that is connected to a smartphone, transmitting radio waves below the skin surface of a person, at the removable smartphone case, receiving radio waves at an antenna array that includes a two-dimensional array of receive antennas, the received radio waves including a reflected portion of the transmitted radio waves, communicating digital data generated in response to the received radio waves from the removable smartphone case to the smartphone, at the smartphone, determining an alignment of the antenna array relative to a vein in the person in response to the digital data received from the removable smartphone case, and at the smartphone, outputting an indicator of alignment from the smartphone in response to the determined alignment.
