  The performance of different chipless RFID tag topologies are analysed in
terms of Radar Cross Section (RCS) and Bit Error Rate (BER). It is shown that
the BER is mainly determined by the tag Radar Cross Section (RCS) once that a
standard reading scenario is considered and a fixed size of the tag is chosen.
It is shown that the arrangement of the resonators in the chipless tag plays a
crucial role in determining the cross-polar RCS of the tag. The RCS of the tag
is computed theoretically by using array theory where each resonator is treated
as a separate scatterer completely characterized by a specific reflection
coefficient. Several resonators arrangements (periodic and non-periodic) are
compared, keeping the physical area of the tag fixed. Theoretical and
experimental analysis demonstrate that the periodic configuration guarantees
the maximum achievable RCS thus providing a global lower BER of the chipless
RFID communication system. We believe that the BER is the more meaningful and
fair figure of merit for comparing the performance of different tags than
bit/cm2 or bit/Hz since the increase of encoded information of the tag is
useful only if it can be correctly decoded.
