Antenna systems for passive RFID tags

An antenna system for a radio-frequency identification (RFID) tag that includes an integrated circuit (IC), comprising:

• an antenna substrate having a proximal end and a distal end;
• a first serpentine antenna element and a second serpentine antenna element, the first and second serpentine antenna elements each supported by the antenna substrate and each having a proximal end and a distal end;
• first and second antenna feed points arranged at the antenna substrate proximal end and connected to the respective proximal ends of the first and second serpentine antenna elements so as to provide an electrical connection to the IC, which is arranged adjacent the antenna substrate proximal end;
• a conducting wire electrically connected to either the first or second serpentine antenna element or the first or second antenna feed point, such that the antenna length of either the first or second serpentine antenna element is longer than the antenna length of the second or first serpentine antenna element, respectively;
• and
• a shunt electrically connected to the first and second serpentine antenna elements or one of the first and second serpentine antenna elements and the conducting wire, the shunt configured to facilitate impedance matching between the antenna system and the IC.

An antenna system for a radio-frequency identification (RFID) tag that includes an integrated circuit (IC), comprising:

• an antenna substrate having a proximal end and a distal end;
• a first serpentine antenna element and a second serpentine antenna element, the first and second serpentine antenna elements each supported by the antenna substrate and each having a proximal end and a distal end;
• first and second antenna feed points arranged at the antenna substrate proximal end and electrically connected to the respective proximal ends of the first and second serpentine antenna elements so as to provide an electrical connection to the IC, which is arranged adjacent the antenna substrate proximal end;
• a conducting wire electrically connected to either the first or second serpentine antenna element or the first or second antenna feed point, such that the antenna length of either the first or second serpentine antenna element is longer than the antenna length of the second or first serpentine antenna element, respectively;
• an impedance-matching circuit electrically connected to one of the first and second serpentine antenna elements and configured to facilitate impedance-matching and current flow between the antenna system and the IC;
• and
• a shunt electrically connected to the first and second serpentine antenna elements and configured to facilitate impedance matching between the antenna system and the IC.