This article presents a comparison between the read range of classical radio frequency identification (RFID) and chipless RFID in free-space and real environments (REs). From the presented model, read range is derived using analytical formulation over nonisolated channels for both technologies. This article shows that the well-known bounds classically used in free space cannot be achieved in REs, i.e., subjected to leakage, coupling, and/or reflections) and therefore need to be modified. Although the introduced bound for semipassive tags is close to the one corresponding to free space, however, we show that for chipless tags, read range cannot be predicted by the radar equation and presents severe limitations since these tags are linear time-invariant systems. This new bound does not depend on the transmitted power or the reader sensitivity but relies on the concept of residual environment. We show that this quantity is the key parameter to evaluate the read range of a chipless RFID system. Moreover, the residual environment can easily be estimated or measured for any reading system. We show that the proposed bound can accurately predict the read range of a chipless system in different environments from anechoic chamber to nonstationary REs. Results are confirmed in simulation and measurements where the difference between the theoretical read range and the measured one is only 20 cm.

Differential RCS characterizes the aptitude of a tag to modulate the backscattered power. This parameter is classically estimated based on the variation of the IQ channels in the time domain. This paper introduces a generalization of the RCS backscattered by a tag and a new definition of the delta RCS in the frequency domain. The analytical model is based on schochastic processes and allows to estimate the delta RCS from the power spectral density of the modulated signal backscattered by the tag. The associated measurement is compared to the classical time domain based methods. Results shows a good agreement with a difference between the different approaches less than 0.5 dB. Finally, the proposed method relies on simple synchronization between the emitter and receiver to estimate the delta RCS while maintaining the accuracy.

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.

This paper presents a contactless approach to characterize coplanar stripline discontinuities based on a radar cross section measurement method. With this approach, the values of the equivalent lumped element models are determined for two discontinuities often encountered in practice: open circuit and short circuit. The discontinuities are incorporated into two different very simple resonators. But contrarily to what is usually done, here the resonators are considered as radar resonant targets and are illuminated by a plane wave. The incremental electrical length due to the discontinuities causes a shift of the resonance frequency, which is used for the extraction of the parameters. The values obtained from full-wave simulations are compared to measurements and to other data available from previous studies.

This paper presents a new reading method which is able to decode the backscattered signal of a chipless tag without any assumption on its orientation. The method is analytically justified by a model and can be applied to any known scatterers or chipless tags composed of multiple resonators. The presented approach is based on two orthogonal measurements in co-polarization on the reader part and can be optionally combined with time gating. Finally, read range is not reduced with this method since the entire energy of the chipless tag’s antenna mode is exploited by the reader.

Only a few efforts have been made to design small scatterers with special polarimetric properties. In this article, the possibility of designing a planar single-layer resonant scatterer presenting roll-invariant cross polarization is demonstrated for the first time. The invariance condition for a general scatterer is first derived analytically from the scattering matrix for copolarization and cross polarization. Then, a design method for a resonant scatterer made from two dipoles with unique angular and phase arrangement is presented. The first step of the design is done theoretically using field superposition. The effects of the coupling between the dipoles and the finite ground plane size are taken into account in a second step by simulation. Two scatterers operating at 4.26 and 5.26 GHz have been manufactured and measured providing good performance with a relative variation of their cross polarization component lower than -2 and -2.7 dB, respectively. Finally, the scattering matrix corresponding to the current design is compared with other classical targets.