Chipless RFID Polarimetric Radar Barcodes Encoded by Dipole Scattering Domains

Recently, a novel chipless radio-frequency identification (RFID) concept based on polarimetric radar barcodes was introduced. These tags are similar to the well known optical quick response codes (QR codes). In polarimetric radar barcodes the information is stored as polarimetrically coded areas arranged in a grid and read out by an imaging radar. This paper presents a novel concept for elegantly creating polarimetric barcodes based on dipole scattering domains. Each scattering domain consists of several hundred dipoles. The dipoles are either uniformly arranged at a specific angle, which produces a specific angle-dependent polarization response, or randomly oriented to produce an unpolarized response. In order to read out the polarimetric information stored in the tags, the position and rotation of the radar barcodes needs to be determined. Our research reveals that using three reference elements and a novel decoding algorithm, a position- and rotation-tolerant readout is possible. To reduce distortions caused by the surface of the structure carrying the dipoles, different matching layer concepts were investigated. The novel chipless RFID tag concept is tested using a fully polarimetric W-band (75-$110 \,\mathrm{G}\mathrm{Hz}$) imaging radar. The implemented setup allows for a theoretical data capacity of $1.92 \,\mathrm{bit} \mathrm{/}\mathrm{c}\mathrm{m}^{2}\,$ on a single layer PCB. In our measurements, we achieved a data capacity of $1.52 \,\,\mathrm{bit} \mathrm{/}\mathrm{c}\mathrm{m}^{2}\,$. Utilizing the chosen tag size of $45 \,\mathrm{m}\mathrm{m} \times 45 \,\mathrm{m}\mathrm{m}$ resulted in a tag with a greater than 30 bit data capacity, which is an excellent value for chipless RFID.