An antenna for use with a Radio Frequency Identification, RFID, tag. A well-known, simple "patch antenna" is formed by two metallic plates, one larger than the other, between which is sandwiched a dielectric sheet. Under the invention, the larger metallic plate is provided by the wall of a metallic shipping container. Thus, one form of the invention includes (1) the smaller metallic sheet, (2) the dielectric sheet, and (3) an RFID circuit. When the dielectric sheet is attached to the wall of the shipping container, a patch antenna is generated which the RFID circuit can use.