Depolarizing Chipless RFID Tag Made Orientation Insensitive by Using Ground Plane Interaction

The ground plane has never been considered as a degree of freedom to be used for chipless radio frequency (RF) identification (RFID) tag design purposes. For the first time, we show that the interaction with the ground plane can be exploited to achieve challenging designs, such as depolarizing tag insensitive to orientation (i.e., nonzero cross polar for any roll angle). The principle relies on the perturbation of the ground plane symmetry with merely one microstrip dipole placed near the edge of the substrate. Chipless RFID tags are realized using three different shapes of the substrate (square, octagonal, and circular) to achieve multiple edges. The measurements are performed in a semianechoic and office environment with tag attached to objects (cardboard box and metallic plate). The measured results of the square chipless RFID tags present magnitude variations (< 10 dB) but are detectable over a full 360° even in real environment yielding an “orientation-insensitive” detection system. Compared to previous designs, the frequency variability of the peaks is negligible.