In one embodiment, an antenna configuration for locating RFID tags has two sets of (mutually orthogonal) elongated reader coils, where each elongated reader coil corresponds to two or more different possible locations of RFID tags, and each possible location is associated with one reader coil in each of the two sets. The identities and locations of RFID tags can be determined by (sequentially) energizing the different sets of reader coils and correlating the recorded responses from RFID tags. In one application, the antenna configuration is used at the box level of a cold storage system for biological samples having one or more freezers, each freezer having one or racks, each rack receiving one or more boxes, each box receiving one or more sample containers, where, in addition to the biological sample, each sample container has a unique passive RFID tag.