Wireless identification tag having circularly polarized planar antenna

A wireless identification tag having a circularly polarized planar antenna, the wireless identification tag comprising:

• an electrically conductive substrate, comprising:
• a first slot portion stretching along a first direction in parallel with the electrically conductive substrate, wherein the first slot portion substantially passes through the electrically conductive substrate and has a first width;
• a second slot portion stretching along a second direction in parallel with the conductive substrate, wherein the second slot portion substantially passes through the electrically conductive substrate and has a second width, and an angle between the first direction and the second direction is substantially between 45 degrees and 135 degrees;
• and
• a third slot portion connected between the first slot portion and the second slot portion, wherein the third slot portion substantially passes through the electrically conductive substrate and has a third width;
• and
• a wireless identification device used to receive or transmit an electromagnetic wave signal, wherein the wireless identification device is disposed in the first slot portion or the second slot portion.