A novel chipless radio frequency identification（ RFID） tag with high coding capacity is designed. Two groups of M-type slot resonators with a property of orthogonal polarization make up this tag. The tag is more compact and has a high Q factor of radar cross-section（ RCS） magnitude. The coding capacity of the tag in the fixed ultra wide band（ UWB） band is increased by six times by the polarization multiplexing and frequency shift coding technique under the excitation of ± 45°polarized waves

the 24 bit encoding capacity can be achieved in a compact size of 12 mm × 18 mm.