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We propose a new approach based on the multicarrier system, in which multiple narrowband pulses emit toward a chipless RFID tag in the UWB, to decode the tag in the time domain. The multicarrier system is known to be able to reduce complexity and interference, and also increase spectrum efficiency and flexibility. In this study, we not only experimentally investigate the backscattered signal of a frequency-coded chipless RFID tag interrogated by narrowband pulses, but we have also derived mathematical equations to describe the tag responses. We have found that the shape of the reflected response from the tag is determined by the emitted signal multiplied by a distortion factor. The distortion amount depends on transmitted signal bandwidth, tag quality factor, and resonance frequency. We further use the distorted tag response as a tag signature in the time domain for decoding purposes, eliminating the signal transformation to the frequency spectrum, which is one of the most time-consuming post-processing algorithms. To further demonstrate the performance of the proposed approach in a more realistic scenario, we have developed a customized multicarrier transceiver to decode a four-bit cross-polarized tag in the time domain. We have demonstrated that the proposed analytical approach can also enhance tag detection in a realistic environment with multiple parasitic reflections. [ABSTRACT FROM AUTHOR]

A mathematical model to characterize a frequency-coded chipless radio frequency identification (RFID) is presented. A chipless tag is comprised of multiple high-quality factor resonators. The model exploits the bandpass and band-stop characteristics of a frequency-coded tag and the channel model of the reader and tag system. The proposed model accurately reconstructs the time and frequency responses of the tag read by a reader antenna. The model is universal to any type of chipless tag. To validate the model, first, a tag is designed with CST Microwave Studio, a full-wave electromagnetic solver, and its resonant characteristic is extracted. The model is used to validate the simulation and measurement results of the same tag. Also, the tag is measured in a cluttered environment. The results show that the tag is successfully decoded in the presence of a relatively large metallic reflector to verify the robustness of the model, without any calibration. The investigation provides a comprehensive understanding of the tag and the reader system, and it is a step toward reading a chipless tag in a realistic environment. [ABSTRACT FROM AUTHOR]

Eliminating the strong self-interference signal in chipless radio frequency identification (RFID) readers is key for enabling a reliable and long range reading in chipless RFID readers. The suggested method is to add a compensation signal to cancel the leakage signal vectorially before the first stage of the receiver front-end. An ultra-wideband (UWB) polyphase power divider (PPPD) generates the vector compensation signal of any arbitrary amplitude and phase. Unfortunately, the reported PPPD cannot meet the requirements for the realization of a UWB compensation unit (CU). A microstrip wideband differential phase shifter capable of producing a wide range of phase shifts is presented in this paper. The delay lines, including transmission line (TL) segments loaded with shorted stubs (SSs), generate prescribed phase shift values with respect to the universal reference line. It is shown that an arbitrary phase shift (up to 360°) with an in-band return loss (RL) better than 15 dB within an octave bandwidth is obtainable. Its full-range phase shift capability alongside the universal reference line and simple structure ensure its suitability for polyphase applications. To verify the proposed structure, a set of C-band phase shifters ranging from 60° to 300° is designed and fabricated, and a phase deviation from ±1° to ±9° is obtained. Finally, based on the proposed differential phase shifter, a four-phase power divider is implemented and utilized in the CU of a chipless RFID reader. Excessive isolation of better than 35 dB over 4–8-GHz frequency band is attained. [ABSTRACT FROM AUTHOR]

Frequency-domain chipless RFID readers hold tremendous promise as a low-cost solution for mass production of this technology. However, the strong self-jamming signal leakage, from the transmitter to the receiver, significantly degrades the sensitivity of the reader. As a result, the maximum reading range of the system is diminished. To address this issue, we studied the sources of interference signals in the system and proposed a method to significantly reduce them. An ultrawideband compensator, over the wide frequency range of 4.3 to 7.3 GHz, was designed and implemented. This method realized an interference isolation better than 40, 55, and 55 dB in single-antenna, dual-polarized antenna, and two-antenna readers, respectively. A noticeable 25-dB excessive isolation to that of the conventional architecture which should help to bring this technology closer to commercial adoption. [ABSTRACT FROM AUTHOR]

Spatial diversity cross-polar approach to fast electromagnetic imaging of millimeter-wave chipless radio-frequency identification (RFID) tags is proposed. Slow imaging in the synthetic aperture radar (SAR) technique due to the moving reader antenna is replaced by a stationary multiple-input multiple-output (MIMO) array antenna. The proposed MIMO technique requires a large number of antenna elements, which impedes practical implementation of the reader. An optimized MIMO system through a genetic algorithm halves the number of antenna elements and successfully replaces the conventional SAR. The optimized antenna system combines with the original spatial diversity approach to provide a low-cost solution for chipless RFID tagging with enhanced content capacity. The system successfully decodes a 60-GHz 17-b chipless tag in an area that is one fifth of a credit card. The tag can be printed with a low-resolution printer and read on metal and liquid containers. [ABSTRACT FROM AUTHOR]

A novel compact printable dual-polarized (DP) chipless radio-frequency identification (RFID) tag is presented along with its real-world implementation challenges. First, the DP tag with simulation and measurement results is presented, where ‘U’ shaped slot resonators are re-used in both vertical (V) and horizontal (H) polarizations to double the encoding capacity within a fixed bandwidth. Next, slot-length variation encoding technique is added to reduce the tag size by 50%. After that, a 16-bit proof of concept DP tag is developed that achieved 16.6 bits/cm^2 data density, which is the highest among the reported works. Next, a step-by-step guideline is presented to overcome the real-world challenges for implementing printable chipless RFID tags, which starts with a detail study on the effect of ink conductivity, and permittivity and loss tangent of the substrate on the tag performance. Then, a quick approximate substrate characterization technique is presented, which is verified by measurement of thermal printed patch tags. Finally, tag printing procedure on paper using a thermal printer is briefed, which is followed by a discussion on some printing inaccuracies and their plausible solutions. All these analysis will build a firm understanding and practical insight on implementing the proposed promising conductive ink printed chipless RFID tag for identification, authentication and sensing. [ABSTRACT FROM PUBLISHER]

Two novel compact printable chipless RFID systems are presented, which are: 1) a dual-polarized (DP) system and 2) an orientation insensitive (OI) system. Chipless tags for both the DP and OI systems consist of horizontally (H) and vertically (V) polarized “I” shaped slot resonators of different lengths, which create frequency signatures in the backscattered signal. Here, different V–H slots are used in the DP tag to double the encoding capacity within a fixed bandwidth and same V–H slots are used in the OI tag to achieve orientation insensitivity. Next, for reading these DP and OI tags, a low-profile low-cost wideband DP aperture coupled microstrip patch antenna (ACMPA) with high port-to-port isolation is developed as well. A reader with DP transmission and reception is capable of reading both the DP and OI tags. These single-sided compact tags are directly printable using conductive ink. Here, DP tags with double data capacity are suitable for fixed orientation applications demanding high data capacity, whereas OI tags are suitable for low data capacity applications requiring orientation insensitivity. Moreover, the developed commercially suitable DP ACMPA can also be used universally for reading all other frequency-domain-based tags. [ABSTRACT FROM PUBLISHER]

A novel localization technique for frequency-domain chipless RF identification (RFID) tag is proposed. A short-duration ultra-wideband impulse radio signal interrogates the tags, and multiple receivers in the interrogation zone capture the backscattered signal from the tags. The received signals from the chipless tags are analyzed for the structural mode radar cross section to determine the relative ranges. Using the range information, the linear least square (LLS) method is employed for accurate localization of tagged items. The accuracy of the localization method is analyzed by moving the chipless tag within a fixed interrogation zone. The whole system is modeled in CST Microwave Studio Suite 2012 to comply with a realistic scenario. The post-processing for range and tag position estimation through LLS is done in MATLAB. The method is also verified in laboratory environment with fabricated chipless RFID tags and multiple receiving units. The range and angular resolution are 2.1 cm and 3.5^\circ, respectively. The analysis and results create a strong foundation for chipless RFID tags to be used in tracking and localization. [ABSTRACT FROM PUBLISHER]

A novel approach is presented to accurately estimate the resonant features of a multipatch backscatter-based chipless radio frequency identification (RFID) tag. An ultra-wideband impulse radar (UWB-IR)-based reader interrogates the chipless tag with a UWB pulse, and the received backscatter is analyzed in the time domain. The key components constituting the backscattered signal, the structural mode, and the antenna mode are identified, and their spectral content are analyzed. Analysis shows that the antenna mode backscatter contains the information carrying signal while the structural mode backscatter contains no information about the tag. A semi-analytical model is developed to explain the behavior of the signal backscattered from the chipless RFID tag. Simulation and semi-analytical results are validated by experimental measurements obtained in an anechoic chamber environment using a 4-b multipatch chipless RFID tag. The new method does not rely on calibration tags for operation and has a greater degree of freedom in the orientation of tags with respect to a reader. A novel method, selective spectral interrogation (SSI), that uses a set of interrogation pulses to extract information bits stored in the spectral signature of the chipless tag is also introduced. [ABSTRACT FROM AUTHOR]

A very low-cost RFID reader architecture comprised of a voltage-controlled oscillator (VCO), a mixer, and a low-pass filter (LPF) for reading an ultra-wideband chipless RFID tag is proposed. The VCO generates a linear chirp (swept) frequency interrogation signal. The reader, which is a coherent frequency-modulated continuous-wave radar, interrogates a tag and decodes the tag's identification data in both amplitude and phase information. A signal-processing technique based on Hilbert transform (HT) is used and accurate detection of a 9-b tag is achieved. The new reader needs only one VCO and does not need any calibration tag to decode data as needed for its predecessors. [ABSTRACT FROM PUBLISHER]

A novel compact design of an ultralow-cost fully printable slot-loaded dual-polarized chipless radio frequency identication tag is presented with four near- and far-field reading techniques. The tag consists of four rectangular metallic patches loaded with multiple slot resonators. Slots with the same polarization for adjacent frequencies are placed alternately into two patches to reduce the mutual coupling between the slots. Then two similar sets are placed in horizontal and vertical polarizations to double the number of bits within the same frequency bandwidth. The tag can be detected using dual-polarized waveguide(s) or dual-polarized antennas. This single-sided compact chipless tag has higher data capacity and lower cost compared with the existing printable chipless tags and can be used in personal ID or credit cards and banknotes and can be directly printed on paper or plastic packets for item-level tagging. [ABSTRACT FROM AUTHOR]

A fully passive printable chipless RFID system is presented. The chipless tag uses the amplitude and phase of the spectral signature of a multiresonator circuit and provides 1 : 1 correspondence of data bits. The tag comprises of a microstrip spiral multiresonator and cross-polarized transmitting and receiving microstrip ultra-wideband disc loaded monopole antennas. The reader antenna is a log periodic dipole antenna with average 5.5-dBi gain. Firstly, a 6-bit chipless tag is designed to encode 000000 and 010101 IDs. Finally, a 35-bit chipless tag based on the same principle is presented. The tag has potentials for low-cost item tagging such as banknotes and secured documents. [ABSTRACT FROM AUTHOR]

A quasi-static equivalent-circuit model of a dumbbell-shaped defected ground structure is developed. The equivalent-circuit model is derived from the equivalent inductance and capacitance developed due to the perturbed return current path on the ground and the narrow gap, respectively. The theory is validated against the commercial full-wave solver CST Microwave Studio. Finally, the calculated results are compared with the measured results. Good agreement between the theory, the commercially available numerical analyses, and the experimental results validates the developed theoretical model. [ABSTRACT FROM AUTHOR]

Investigates the nonuniform photonic-bandgap (PBG) microstripline low-pass filters. Characteristics of planar PBG; Design of microstrip PBG; Theory of nonuniform microstrip PBG; Binomial distribution of circular-patterned PBG.