Realistic frequency coded chipless RFID: physically modulated tags and refectarray readers

Recently, the chipless Radio Frequency Identiﬁcation (RFID) technology has attracted tremendous attention in the market of item identiﬁcation where the cost is the main concern. However, up to date the technology is at the conceptual level and suffers from a lot of imitations that hinder the technology deployment. The chipless RFID system comprises three major parts which are the reader circuit, the interrogation antennas, and the chipless tags. The contributions of this dissertation are to overcome the challenges that impede the deployment of the chipless RFID system from the perspective of innovating physically modulated tags and developing the reader antenna system. In particular, the system is considered in three novel aspects. The ﬁrst aspect is the linear physically modulated tags where the tag is interrogated by Ultra Wideband (UWB) signal and the tag inscribed metallic resonators are physically modulating the interrogation frequencies. Therefore, the UWB waveform is modulated in the form of resonant notches, and/or peaks that are inherently embedded in the tag backscattered Radar Cross Section (RCS) frequency response. In this regard, four innovative physically modulated tags are developed aiming at enhancing the coding efﬁciency, maximizing the coding capacity, conserving the operating frequency range and preserving the tag size. The ﬁrst tag is based on nested circular ring resonators where each resonator codiﬁes a tag coding notch. Terefore, the tag structure is scalable, printable and compact size. Moreover, a novel encoding methodology is employed to preserve the notch width and position while coding. The second developed tag is a depolarizing one where the polarization isolation between the reader interrogation signal and the tag response is utilized to minimize the environmental clutter reﬂections. Furthermore, the tag is scalable, printable, and compact size in the credit card format. Thirdly, a novel Notch Width Modulation (NWM) tag is introduced where the tag-ID is not only based on the notch position but also on the notch width. Hence, the notch width conﬁgures a further dimension to increase the Degree of Freedom (DoF) for coding and modulation. Therefore, the notch width and position are modulated simultaneously aiming at enhancing the coding efﬁciency and capacity. Lastly, a novel On Off Notch/Peak (OO-N/P) and Notch/Peak-Position (N/P-P) modulation tag is introduced. The tag basic idea is to exploit both the co-polarized and cross polarized backscattered signals from a tag excited with a linear polarized wave. Consequently, the tag signature is encoded into Notch/Peak (N/P) format in two orthogonal planes. Thus, the Co/Cross-polarizing N/P modulation scheme presents a novel criterion for enhancing the coding efﬁciency and capacity of the chipless RFID systems. Moreover, the cross-polarized response enhances the tag detection in a realistic environment. The proposed tags and their associated physical modulation schemes are validated using Electro Magnetic (EM) simulations and real-world testbed measurements. In the second aspect, the Reﬂectarray (RA) antenna is proposed to be utilized in the reader side aiming at increasing the reading range, minimizing the environmental reﬂections, and acquiring a lot of novel capabilities that can not be provided by the conventional antenna arrays. The spatial feeding RA antenna is easily integrated with the RF circuits, lightweight, conformal geometry, and low cost. Hence, in this concern, three different novel designs are developed. The ﬁrst design utilizes the Log Periodic Array (LPDA) antenna to feed the developed RA surface. This introduced prototype operates at 5.8GHz and achieves 300MHz bandwidth. Moreover, the RA antenna radiation beam is 4 times narrower than the feeder beam and thus 6dB higher in gain with −10dB Side Lobe Level (SLL). The second developed prototype uses a constant phase center horn antenna to feed the RA surface. Thus, an UWB RA antenna enabling multiple bits accommodation is designed. This antenna operates from 4GHz to 6GHz with 15° Half Power Beam Width (HPBW), 19dBi gain, and −10dB SLL. Furthermore, this developed UWB RA antenna is successfully integrated with the physically modulated tags and a reading range of 1m is achieved. To the best of my knowledge, this is the highest reading range achieved in the Frequency Coded (FC) chipless RFID systems, considering real-world indoor environment and software deﬁned radio reader. After that, dual-polarized RA antenna with low cross-polarization level is presented. This RA antenna is proposed to be utilized with the Co/Cross-polarizing tags. Finally, a successful implementation of an electronic beam steering RA antenna is introduced. This novel beam steering RA antenna system enhances the reading robustness and can precisely locate the chipless tags. In this concern, a novel unit cell that is able to electronically control the reﬂected phase at different discrete frequencies utilizing a single varactor diode is proposed. Therefore, a scanning range of ±50° is achieved. Moreover, the steered beams are 4 times narrower than the feeder beam and thus 4 times higher in gain. In the third aspect, the nonlinear physically modulated tags are proposed. The core functionality relies on interrogating the tag with a prescribed set and format of frequencies in a time regulated technique while the tag replies with its unique ID at other frequencies. Therefore, the nonlinearity is exploited to completely isolate the environmental clutter reﬂections, get rid of the necessary reference calibration measurements, overcome the detuning caused by the tagged item materials, and increase the coverage. These objectives are attained by exploiting the nonlinearity generated from a single unbiased diode integrated with the tag structure. The ﬁrst proposed tag category relies on exploiting the second order nonlinear terms. Therefore, in this regard, three novel tags are introduced. The ﬁrst class is the single tone harmonic radar tags. In this class, the reader scans the available tags by sending speciﬁc fundamental tones. Then, the tag receiving antenna is tuned at only one of these fundamentals which is maximally conveyed to the nonlinear device for generating the corresponding harmonics. Consequently, the tag transmitting antenna is tuned at the second harmonic which is retransmitted back towards the reader representing the tag-ID. Thus, the narrower is the band-pass ﬁlter provided by the tag receiving antenna or integrated into it, the more the frequencies that can be utilized for coding. After that, the multi-tone interrogation is proposed to increase the coding capacity. Hence, the tag is interrogated with a prescribed set of fundamentals that are swept over the time to avoid the generation of the mixing products in the reader and tag as well. The tag in turn which is completely planar based on the Coplanar Waveguide (CPW) technology implements a Notch Position Modulation (NPM) scheme in the second harmonics of these fundamental tones. Therefore, the notches that are existing in the second harmonic response symbolize the tag-ID. Afterward, the simultaneous multi-tone interrogation is explored. In this concern, a set of distinct frequency pairs are used to interrogate the nonlinear tags. As a consequence, these tones are mixed through the nonlinear device. Consequently, the tag transmitting antenna ﬁgures out only one of these mixed products. The second proposed tag category relies on exploiting the inter-modulation communication principle which exhibits a small frequency span. Therefore, the tag is illuminated by two co-located frequencies and respond at an inter-modulated frequency which is retransmitted by the tag transmitting antenna representing the tag-ID. Finally, the phase encoding capability is proposed. Therefore, not only the existence or the non-existence of a harmonic notch or peak used in coding the tag-ID but also the corresponding relative phase states can be considered. The introduced tags and their associated physical modulation schemes are veriﬁed using harmonic balance analysis, EM simulations and realistic testbed measurements. Lastly, the unique features which are considered in the dissertation bring a signiﬁcant enhancement to the deployment of the chipless RFID system.