A novel tristate coupled line microstrip resonator is proposed for compact chipless radiofrequency identification tags. The proposed resonator can be reconfigured to present one of the three possible states: 00, 10, and 01, which denote no resonance, resonance at f1, and resonance at f2, respectively. The resonator can be designed with f1 and f2 at appropriate positions, reducing the required spectrum. A multiresonator prototype consisting of 14 elements of the proposed resonator is designed, analyzed, and experimentally characterized. This prototype is implemented on an RT Duroid 5880 substrate with a dielectric constant of 2.2 and a thickness of 0.78 mm. The prototype can be reconfigured for 314 codes. A test‐bench comprising six resonators and transmitting and receiving wideband antennas is established and used to experimentally characterize a prototype tag. The experimental results exhibit good agreement with the simulation.
This paper presents a new, compact, high-coding-capacity resonator suitable for applications in chipless RFID tags. These tags consist of multiple resonators and two cross-polarized ultra-wide band antennas. Each resonator contains a U-shaped coupled microstrip frame with isolated (K-1) legs inside. One of the legs is designed to be connected to the U-frame via a metallic strip in order to adjust its resonance frequency. Using this feature, the frequency of each resonator can be reconfigured to be equal to one of the K-resonance frequencies. Therefore, each resonance presents one of the Kstates of the resonator. This allows each resonator to represent more than one bit of information; this arrangement also permits N resonators tags to provide K N codes. The structure can store large volumes of data in a small area and can simplify the detection process by only reading N resonance frequencies for each code. When N resonator tags are used in the proposed structure, the amount of data that can be encoded increases to 2 (log K / log 2)N compared to 2 N in the case of conventional one-bit resonator (2-states) tags. An additional arrangement is also proposed and investigated in order to improve the spectral efficiency by allowing the bandwidth of each single resonator to be shared between two resonators. Several tags for codes with K = 8 are designed and implemented on the RT Duroid 5880 substrate as a proof-of-concept. An 8-state of the proposed resonator can be implemented in an area that is almost the same size as the area of a conventional 2-state resonator operating at 5 GHz. A satisfactory agreement between the empirical and simulated results is then confirmed.INDEX TERMS K-state resonator, high coding capacity, chipless RFID, ultra-wideband antenna (UWB), Internet of Things (IoT).
A compact four-element dual-band multiple-input and multiple-output (MIMO) antenna system is proposed to achieve high isolation and low channel capacity loss. The MIMO antenna was designed and optimized to cover the dual-frequency bands; the first frequency band is a wide band, and it covers the frequency range of 1550–2650 MHz, while the other frequency band covers the 3350–3650 MHz range. The measured wide-band impedance bandwidths of 1.1 GHz and 300 MHz were achieved in the lower and upper frequency bands, respectively. The proposed structure consists of four novel antenna elements, along with a plus-sign-shaped ground structure on an FR4 substrate. The overall electrical size of the whole dual-band MIMO antenna system is 0.3λ(W) × 0.3λ(L) × 0.008λ(H) for the lower frequency band. It achieved greater than 10 and 19 dB isolation in the lower and upper frequency bands, respectively. The antenna system accomplished an envelope correlation coefficient of |ρ|≤0.08 in the lower frequency band, while it achieved |ρ|≤0.02 in the higher frequency band. The computed channel capacity loss remained less than almost 0.4 bits/s/Hz in both frequency bands. Therefore, it achieved good performance in both frequency bands, with the additional advantage of a compact size. The proposed MIMO antenna is suitable for compact handheld devices and smartphones used for GSM (Global System for Mobiles), UMTS (Universal Mobile Telecommunications Service), WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution), 5G sub-6 GHz, PCS (Personal Communications Service), and WLAN (wireless local area network) applications.
A novel and compact dual-polarized (DP) chipless radio-frequency identification (RFID) tag is presented in this paper. This tag can read both vertical and horizontal orientations within its frequency band, which improves the robustness and detection capability of the RFID system. The proposed tag makes use of the slot length variation encoding technique to improve the encoding capacity. This technique can duplicate the encoding capacity, thereby reducing the overall tag size by almost 50%. In particular, the proposed tag has an encoding capacity of 20 bits in the 3–8 GHz frequency band and achieves data density of around 15.15 bits/cm2. Three prototypes are fabricated and tested outside an anechoic chamber. Furthermore, one tag is tested at different distances (10 cm, 30 cm, and 60 cm) from the reader and the measured results are compared. The simulated and measured results are in reasonable agreement, with acceptable shifts at some frequencies due to fabrication and experimental errors.
This paper presents novel low-cost single- and dual-band microstrip patch antennas. The proposed antennas are realized on a square microstrip patch etched symmetrically with four slots. The antenna is designed to have low cost and reduced size to use in Internet of things (IoT) applications. The antennas provide a reconfigurable architecture that allows operation in different wireless communication bands. The proposed structure can be adjusted to operate either in single band or in dual-band operation. Two prototypes are implemented and evaluated. The first structure works at a single resonance frequency (f1 = 2.4 GHz); however, the second configuration works at two resonance frequencies (f1 = 2.4 GHz and f2 = 2.8 GHz) within the same size. These antennas use a low-cost FR-4 dielectric substrate. The 2.4 GHz is allotted for the industrial, scientific, and medical (ISM) band, and the 2.8 GHz is allocated to verify the concept and can be adjusted to meet the user’s requirements. The measurement of the fabricated antennas closely matches the simulated results.
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