A dual band dual antenna with read range enhancement for UHF RFID tags

This article presents a novel dual antenna structure for dual ultra high frequency bands (f₁ = 866 MHz and f₂ = 915 MHz) for radio frequency identification tags. The proposed structure consists of two dual band antennas, one acting as a receiving antenna and the other as a backscattering antenna at both the frequency bands. The receiving antenna is designed to have input impedance complex conjugate to the impedance of tag IC in order to maximize power transfer between the antenna and the microchip. The backscattered antenna is designed to have real‐valued input impedance at both the operating frequency bands to obtain maximum differential radar cross section leading to read range enhancement. The dual band receiving antenna is designed by embedding a pair of thin slits at a radiating edge of inset fed microstrip antenna. The backscattering antenna is comprised of two elements, one is a comb‐shaped open ring element, and the other is a meander line structure which is within the open ring element. Compared to conventional antennas, the proposed dual antenna structure provides a read range enhancement due to improved maximum differential RCS. The proposed dual antenna produced 4.3 m and 6.8 m read range at 866 MHz and 915 MHz, respectively.     

Platform tolerant dual‐band UHF‐RFID tag antenna with enhanced read range using artificial magnetic conductor structures

In this work, a platform tolerant novel dual band tag antenna is proposed for UHF‐RFID bands used in Europe (855‐867 MHz ) and Japan (950‐955 MHz). Asymmetrical shunt stub feed network is employed to effectively match its impedance to the microchip (Alien Higgs‐4). The antenna miniaturization is achieved by embedding inverted L‐shaped slit on left side of the patch. Also, asymmetrical stepped rectangular slot is embedded to further achieve the optimized dual band response at the desired resonant frequencies (f₁ = 866 MHz and f₂ = 953 MHz). To further enhance its radiation performance on conductive objects like metallic surfaces, the proposed tag is integrated with artificial magnetic conductor (AMC) structure. Also, antenna parameters such as main lobe gain, directivity, front‐to‐back ratio parameters are examined for the integrated tag in free space and on metallic sheet. The proposed integrated tag exhibits directional radiation pattern making it insensitive to underlying object and thus platform tolerant. Further, the proposed integrated tag exhibits steady gain response inside the resonating bands on different sized metallic sheets. The proposed integrated tag is compact (2635 mm³) covering European band with a read range of 7.3 m and Japanese band with a read range of 10.8 m.     

A single sided dual‐antenna structure for UHF RFID tag applications

In this article, a dual‐antenna structure is presented for UHF RFID tag. The proposed structure is made of two L‐shaped strip antennas along with a cross‐shaped slot loaded patch. One antenna is exclusively used for receiving and harvesting full energy with complex conjugate of tag chip, whereas another used as backscatter to enhance maximum differential radar cross section with purely real input impedance, which results in the enhancement of read range. Further, electromagnetic band gap structure is used around the dual‐antenna structure to increase the gain which results in improved read range. The proposed antennas are fabricated and the S‐parameters are measured with the help of differential probe technique. Simulation and measurement results are found in good agreement. The performance of the proposed antenna is also investigated when it placed on different materials such as metal, wood, glass, and plastic. The study shows that the read range of antenna increases considerably when it is mounted on a metallic surface, while the maximum performance is observed when the antenna is attached on a glass surface with highest relative permittivity. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:619–628, 2015.     

Long read range and flexible UHF RFID tag antenna made of high conductivity graphene‐based film

An antenna made of a graphene‐based film with organic polyimide precursor of high conductivity 1.1 × 10⁶ S m^?1 and thickness 30 μm, operating in the ultrahigh frequency (UHF) band for radio frequency identification applications is presented in this article. The antenna is optimized to have a conjugate match to the impedance of the chip by tuning the design parameters. Tags are fabricated and tested using the designed antenna, which are shown to have realized gain above ?1.5 dBi and radiation efficiency beyond 90% in the whole UHF band from 860 to 960 MHz. The read range of proposed tag is greater than 12.3 m over the entire UHF band with a maximum value of 14 m at 920 MHz. In addition, the flexibility of the tags is demonstrated. After 2000 cycles of bending and stretching, the read range only decreases by 4.5 m comparing to the initial state at 915 MHz.     

Linearly tapered meander line cross dipole circularly polarized antenna for UHF RFID tag applications

In this article, a circularly polarized antenna for ultra‐high frequency radio frequency identification (RFID) tag is presented. The circular polarization is realized by two orthogonal, unequal length linearly tapered meander line cross dipoles. The meander structure with capacitive tip loading is used for size miniaturization of the antenna. A modified T‐match network is employed to feed the cross dipole structure. The measured 10‐dB return loss bandwidth of the cross dipole antenna is 17 MHz (908‐923 MHz) and the corresponding 3‐dB axial ratio bandwidth is 6 MHz (912‐918 MHz). The overall size of the proposed antenna is 0.17λ₀ × 0.17λ₀ at 915 MHz. The maximum read range between the reader and the tag with the proposed antenna is 4.7 m larger than the analogous linearly polarized tag antenna due to the reduction in polarization loss between the tag and reader antennas. Thus, a maximum read range of 15.66 m with the gain of 1.28 dBic is achieved at 915 MHz.     

Linearly tapered meander line broadband monopole tag antenna with T‐match for Ultra High Frequency Radio Frequency Identification applications

In this paper, a compact, broadband linearly tapered meandered monopole tag antenna for UHF‐RFID is designed and optimized using particle swarm optimization (PSO) algorithm. An inductive T‐match network is utilized for impedance matching with capacitive Higgs‐4 chip. The optimization goal of PSO was conjugate matching and in consequence the maximization of read range. Equivalent circuit of the proposed tag antenna is derived using ADS software to validate its impedance characteristics. The performance of the proposed tag in terms of tag power sensitivity, read range, realized gain, and differential radar cross section has been experimentally characterized. To check the tolerance of the designed tag to various object platforms, its read range performance is also verified on objects like wood, fiber, plastic, and so forth. Furthermore, read pattern of the proposed tag has been measured and found to have figure of eight in E‐plane and omnidirectional in H‐plane. Experimental results reveal that the proposed tag covers 865‐867 MHz (ETSI band, Europe) and 902‐928 MHz (FCC band, United States) both major RFID bands with a read range of 10 and 12 m, respectively. The proposed tag has 2060 mm³ of volumetric size with maximum measured readable distance of 12 m with EIRP of 3.28 W.     

具有感应反馈环的超高频RFID标签天线设计

针对标签天线在RFID系统中的重要性,基于微带天线设计和电磁场散射理论,设计和分析了一种具有感应反馈环的超高频段RFID标签天线。天线的谐振频率为915 MHz,尺寸为78 mm×23 mm,天线显示近线性相位特性,在电压驻波比小于2的条件下,天线的阻抗带宽为100 MHz。可以通过调整感应反馈环的长度来调整天线的谐振频率,天线的增益为2.5 dBi左右。通过仿真和测量可知,这种天线能较好地满足RFID超高频段标签的要求。     

Compact meandered RFID tag antenna with high read range for UHF band applications

In this work, a compact, long read range, and an efficient spiral loop structure coupled tag antenna is proposed for UHF‐RFID applications. Meandered line element is inductively coupled to spiral loop for matching its input impedance to Higgs‐4 chip. Equivalent circuit of antenna is extracted to analyze its working mechanism in the operating band. Experimental characterization validates the performance of proposed tag antenna in free space and on cardboard sheet in terms of read range, tag sensitivity, and differential radar cross section with an EIRP of 3.28 W. The measured radiation pattern of the tag is found to be omnidirectional in H plane and figure of eight in E plane. The tag's read range is measured on objects like fiber, wood, plastic, and glass in outdoor scenario to study its environment tolerance. The tag antenna has volumetric size of 1736 mm³ and read range of 13.6 m in US RFID band.     

A low profile aperture coupled antenna with broadband circular polarization characteristics for UHF RFID applications

An aperture coupled microstrip‐line fed antenna (circular patch) with CP radiation is initially investigated. To achieve good CP radiation at 925 MHz UHF RFID frequency, the technique of loading an inverted C‐shaped slit into the circular patch is initially proposed. By further loading an open eccentric‐ring shaped parasitic element around the circular patch, an additional CP frequency can be excited at 910 MHz, and by combining these two CP frequencies, broad CP bandwidth that can cover the entire 902‐928 MHz UHF RFID band is achieved. Because of the parasitic element, the total dimension of proposed antenna is modified to 170 × 170 × 11.4 mm³. From the measured results, the impedance and CP bandwidths of the proposed antenna were 9.4% (859‐944 MHz) and 3.1% (902‐930 MHz). Furthermore, its corresponding peak gain and efficiency are 5.9 dBic and 84.3%, respectively. Further analyses have shown that the proposed antenna can also achieve good CP frequency agility across the desired UHF RFID operating band (902‐928 MHz).     

Design of a compact size tag antenna based on split ring resonator for UHF RFID application

In this article, a new design of miniaturized split‐ring resonator antenna using a meander line technique with a simple impedance matching method applicable to UHF‐RFID tags is presented. The new approach is based on the integration of a meander line into the radiating element of SRR to reduce the electrical tag size and a theoretical demonstration to calculate the conjugate impedance matching and directly attach the antenna with the chip. The new SRR antenna, which is printed on the flexible substrate Arlon CuClad 250LX, is designed using Alien Higgs 3 RFID ASIC whose input impedance is 25‐j190. The prototype antenna has a low‐cost compact size (18.28 mm × 18.28 mm) with a read range higher than 4 m within the RFID UHF band and with a roughly 4.2‐m peak range at 915 MHz. As a proof of behavior, a tag prototype is fabricated and measured to operate at a UHF RFID band. Based on some works' results, an optimized design is obtained with a 48% size reduction compared with the classic split ring resonator antenna and with a good impedance matching the antenna with RFID ASIC without the need for any external matching network.     

Equilateral triangular patch antenna for UHF RFID applications

This article proposes an equilateral triangule‐shaped patch antenna for radio frequency identification (RFID) applications in the 900 MHz (902–928 MHz) ultra high frequency (UHF) band. To achieve optimal impedance matching and 10‐dB operating bandwidth at the desired band, the L‐shaped probe‐feed technique was used as the feeding structure of the proposed antenna. Furthermore, a near semicircular notch was also loaded into the patch so that good circularly polarized (CP) radiation can be generated from the proposed patch antenna. By simply shifting the position or radius of this notch, the CP frequency can be varied with ease. Here, 10‐dB impedance bandwidth and 3‐dB axial ratio bandwidth of 25 and 3% were achieved. Furthermore, stable gain variation of approximately 6 dBi was also exhibited across the RFID UHF band. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:580–586, 2014.     

A circular patch antenna with parasitic element for UHF RFID applications

This article initially proposes a directly‐fed circular patch antenna with L‐shaped ground plane for Radio Frequency Identification (RFID) applications in the 900 MHz (902?928 MHz) ultrahigh frequency (UHF) band. To achieve circularly polarized (CP) radiation, two arc‐shaped notches are loaded into the main patch. To enhance the CP bandwidth so that the proposed antenna can also cover the UHF RFID band for Europe (866?869 MHz), a parasitic element is printed besides the main patch. Experimental measurements show that the 10‐dB return loss bandwidth of the proposed antenna was 30.95% (833?1138 MHz) and its corresponding 3‐dB axial ratio bandwidth was 8.95% (865?946 MHz). Good gain and radiation efficiency of more than 7 dBic and 90%, respectively, were also exhibited across the two desired UHF RFID bands. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:681–687, 2015.     

Broadband circularly polarized antenna with moon‐shaped parasitic element

A broadband circularly polarized (CP) circular patch antenna with an L‐shaped ground plane and parasitic element is studied. The use of this L‐shaped ground is to achieve short probe feed connection to the circular patch, while maintaining a certain height between the circular patch and ground plane, so that good impedance matching and bandwidth enhancement can be attained. To achieve CP radiation, two notches are initially loaded diagonally into the circular patch, and to further enhance the CP bandwidth, a novel technique of loading a small size moon‐shaped parasitic element into the notched circular patch is proposed. By doing so, the CP bandwidth of proposed antenna can be tremendously increased by approximately 10%. The experimental results show that the proposed CP antenna can yield impedance bandwidth and CP bandwidth of 835–1150 MHz and 839–968 MHz, respectively, with good gain level of 7.6 dBic. Therefore, this proposed wideband CP antenna can be used for UHF (ultrahigh frequency) RFID (radio frequency identification) reader antenna that operates within the universal RFID bands (840 ? 960 MHz). © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:387–395, 2016     

Compact size flexible UHF RFID tag antenna for racing pigeon ring applications

A very small size radio frequency identification (RFID) tag antenna specifically designed for racing pigeon ring applications is proposed. The structure of this UHF tag is a closed‐loop type printed on a 30 × 8 mm² polyimide film of thickness 0.063 mm. Thus, it can be wrapped into a double layer plastic cylindrical ring of size similar to those used for racing pigeon. By simply tuning the inner width of the loop, good conjugate matching between the tag chip input impedance and the tag antenna can be achieved. When mounted onto a real preserved dried pigeon feet specimen, the measured impedance bandwidth of the tag antenna was 901‐929 MHz. Further experimental results have also shown that the proposed antenna has a maximum reading range of up to 50 cm.     

Dual‐band dual‐polarized compact planar monopole antenna for wide axial ratio bandwidth application

In this article, a geometrically simple, microstrip line‐fed planar monopole structure with slanting edge ground plane is designed to realize the dual‐band dual‐polarized operation. The proposed antenna consists of a rotated U‐shaped patch and an electromagnetically coupled L‐shaped parasitic radiating element. Owing to the combination of microstrip line‐fed radiating patch and a slanting‐edge rectangular ground plane on the opposite side of the substrate, the proposed dual‐band antenna can generate broad axial ratio bandwidth (ARBW) in the upper frequency band. The overall dimension of the prototype is only 32 × 32 × 1.6 mm³. The measured results validate that the proposed antenna has two operational frequency bands, 29.84% (1.54‐2.08 GHz) for linearly polarized radiation and 71.85% (3.96‐8.4 GHz) for circularly polarized radiation. Measured result shows that 3‐dB ARBW of the proposed antenna is 73.54% (3.80‐8.22 GHz) in the higher frequency band. It shows that the higher frequency band exhibits a left‐hand circularly polarized radiation in the boresight direction.     

Novel and compact open‐ended CRLH‐TL notch filter

A novel and very small metamaterial notch filter below 900 MHz is proposed in this paper. In the UHF band, compared to the size of the open‐ended quarter‐wavelength stub that is, 0.25 λ_g (42 mm), the length of the proposed filter is 0.07 λ_g (12 mm) approximately five times smaller. The notch filter is realized by a very short 90°‐phase shifter of the CRLH structure with one‐end open‐terminated. The design method is explained theoretically, while the circuit and geometry are simulated and validated through EM simulations and fabrication. The measured results show a high degree of agreement with the simulated results. The results illustrate the notch created at 900 MHz by the filter to avoid the conflict with Z‐wave communication, UHF RFID tag and uplink of GSM‐E. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:247–253, 2016.     

Single‐fed broadband circularly polarized unidirectional antenna using folded plate with parasitic patch for universal UHF RFID readers

This research proposes a simple economical broadband circularly polarized antenna for universal ultra‐high frequency (UHF) RF identification (RFID) readers. The antenna utilizes a folded plate, a two‐corner truncated parasitic patch, and a ground plane. The folded plate, which is fabricated from one single plate, consists of a two‐corner truncated main patch, a wall patch, and a feed line, where the main patch is perpendicular to the wall patch, which is in turn perpendicular to the feed line. The folded plate enables currents to flow with a phase difference. The simulation results achieved an |S₁₁| < ?15 dB of 805–966 MHz (18% bandwidth), a 3‐dB axial ratio (AR) bandwidth of 834–962 MHz (14% AR bandwidth), and a gain higher than 8.6 dBic. The measured results obtained an |S₁₁| < ?15 dB of 806–970 MHz (18%), a 3‐dB AR bandwidth of 816–963 MHz (16%), and a gain greater than 7.8 dBic. The proposed antenna is applicable for universal UHF RFID readers as it covers the entire operating UHF RFID frequency range of 840–960 MHz. The parametric study and evolution of the proposed antenna are detailed in this research paper as well. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:575–587, 2016.     

An SRR based miniature implantable antenna with a slit loaded ground at MedRadio and ISM bands for biotelemetry applications

A miniaturized implantable microstrip split‐ring antenna (IMSRA) is proposed for wireless biotelemetry. The IMSRA takes up a miniaturized volume of 153.35 mm³ (10.5 × 11.5 × 1.27) and provides a dual‐band operation in 360 to 620 MHz and 2.32 to 2.54 GHz that covers The Medical Device Radiocommunications Service (MedRadio) (401‐406 MHz) and Industrial, Scientific, and Medical (ISM) (433‐434 MHz and 2.4‐2.48 GHz) bands. The principal part of the radiator consists of three homocentric split‐ring elements. In addition, three conductor paths located between the split rings are used for precise adjustment of the frequency. In order to reduce the antenna size, a shorting pin is appropriately inserted between one of the metallic rings and the ground plane. The impedance matching of the antenna is improved by the use of a hook‐shaped slit placed on the ground plane. For verification of the in vivo operation, the proposed IMSRA was measured in two separate skin‐mimicking gels for MedRadio and ISM bands. A prototype was also tested in the skin tissue sample of a donor rat. The proposed antenna offers 53% (360 ~ 620 MHz) bandwidth at 490 MHz and 9% (2.32 ~ 2.54 GHz) bandwidth at 2.43 GHz. The IMSRA exhibits well‐behaved radiation patterns and SAR values at the respective bands.     

Compact dual‐band ring dielectric resonator antenna with moon‐shaped defected ground structure for WiMAX/WLAN applications

In this article, compact ring‐shaped dielectric resonator antenna (DRA) along with moon‐shaped defected ground structure (DGS) was studied. The proposed antenna was fed by microstrip line shifted from center position, which excited TE_01δ mode in ring DRA. Moon‐shaped DGS was acting as a radiator and also reduced the size of proposed antenna by an amount of 14.87% (lower frequency band) and 48.77% (upper frequency band). The proposed antenna was designed to resonate at two different frequencies namely 2.24 and 5.82 GHz with a fractional bandwidth of 30.17% and 22.14%, respectively. Based on optimized design parameters, archetype of antenna structure has been constructed and measured successfully, which shows good agreement with simulated ones. The proposed antenna design was suitable for WLAN (2.4/5.2/5.8 GHz); WiMAX (2.5/5.5 GHz); AMSAT (5.6/5.8 GHz); and WAVE (5.9 GHz) bands. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:503–511, 2016.     

Design and development of enhanced bandwidth multi‐frequency slotted antenna for 4G‐LTE/WiMAX/WLAN and S/C/X‐band applications

A multi‐frequency rectangular slot antenna for 4G‐LTE/WiMAX/WLAN and S/C/X‐bands applications is presented. The proposed antenna is comprised of rectangular slot, a pair of E‐shaped stubs, and an inverted T‐shaped stub and excited using staircase feed line. These employed structures help to achieve multiband resonance at four different frequency bands. The proposed multiband slot antenna is simulated, fabricated and tested experimentally. The experimental results show that the antenna resonates at 2.24, 4.2, 5.25, and 9.3 GHz with impedance bandwidth of 640 MHz (2.17‐2.82 GHz) covering WiMAX (802.16e), Space to Earth communications, 4G‐LTE, IEEE 802.11b/g WLAN systems defined for S‐band applications. Also the proposed antenna exhibits bandwidth of 280 MHz (4.1‐4.38 GHz) for Aeronautical and Radio navigation applications, 80 MHz (4.2‐4.28 GHz) for uncoordinated indoor systems,1060 MHz (5.04‐6.1 GHz) for the IEEE 802.11a WLAN system defined for C‐band applications and 2380 MHz (7.9‐10.28 GHz) defined for X‐band applications. Further, the radiation patterns for the designed antenna are measured in anechoic chamber and are found to agree well with simulated results.