Received: 13 September 2020 Revised: December 2020 Accepted: 28 January 2021 First Published: 15 March 2021 DOI: 10.1002/mmce.22595 RESEARCH ARTICLE Compact shorted C-shaped patch antenna for ultrahigh frequency radio frequency identification tags mounted on a metallic plate Minh-Tan Nguyen1,2 | Yi-Fang Lin1 | Chun-Hsien Chang1 | Chien-Hung Chen3 | Hua-Ming Chen1 Institute of Photonics Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan Department of Mechatronics, Dong Nai Technology University, Bien Hoa, Viet Nam Department of Avionics Engineering, R.O.C Air Force Academy, Kaohsiung, Taiwan Correspondence Hua-Ming Chen, Institute of Photonics Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 807, Taiwan Email: hmchen@nkust.edu.tw Abstract This paper describes an ultrahigh frequency (UHF) tag antenna mounted on a metallic plate for radio frequency identification (RFID) The impedance of the proposed antenna can be tuned using various methods The compact patch antenna consists of a C-shaped resonator and a ground plane connected to a small shorting wall and is connected to a feeding loop in the middle of the Cshaped resonator Etching a couple of slits close to the shorting wall and a slot in the center of the C-shaped resonator provided a flexible method for adjustment to match the conjugate impedance with the UCODE 8/8 m chip (13 − j191 Ω at 915 MHz) The optimal design with an overall size of 30 × 30 × mm3 (0.092 λ0 × 0.092 λ0 × 0.0092 λ0) yielded a high power transmission coefficient of 91% and reading range of 6.4 m for the effective isotropic radiated power (EIRP) of 4.0 W when the tag antenna was mounted on a 220 × 220 mm2 metal plate The proposed antenna was designed at standard frequency bands of the Federal Communications Commission (FCC, 902-928 MHz) for North America and Taiwan Antenna fabrication and testing were performed, which revealed that the measured data were in good agreement with the simulation results KEYWORDS C-shaped patch, metal tag antenna, reading range, RFID tag antenna, shorting wall | INTRODUCTION Radio frequency identification (RFID) tags have been used in a wide range of applications, such as in toll tag systems, distribution logistics, the Internet of things, supply chain management, and security systems.1,2 Generally, tag antennas comprise an antenna and an integrated circuit (IC) chip and can operate in the ultrahigh frequency band (UHF) Thus, the reading range can be extended with a low-cost component.3,4 However, when a tag antenna is placed on or close to metal objects, Int J RF Microw Comput Aided Eng 2021;e22595 https://doi.org/10.1002/mmce.22595 antenna performance degrades because of its material characteristics, which negatively affects fundamental antenna properties including input impedances, power transmission coefficients (PTC), gains, and radiation patterns Several methods have been suggested to overcome this problem and improve tag performance Antennas with artificial magnetic conductors (AMCs) were proposed to enhance the gain and radiation patterns Such antennas consist of a radiating patch on the top and an AMC ground plane installed at the bottom.5-8 However, most AMC antennas have a complex layout, large size, wileyonlinelibrary.com/journal/mmce © 2021 Wiley Periodicals LLC of 13 of 13 and are not cost effective Therefore, these antennas are impractical for applications that require a compact antenna To reduce the profile of the tag antenna, a planar inverted-F antenna (PIFA) structure was introduced A PIFA depends on a high impedance surface to reduce the profile.9,10 The input impedance of an IC chip is generally designed with a high quality factor to enhance its sensitivity, and that causes the designed antennas have difficulty gaining the conjugate impedance matching.11-13 Specifically, studies14,15 have attempted to improve impedance matches based on a loaded bar and conductive layer; however, the radiation efficiency is the main problem, and the impedance tuning of tag antennas is difficult Loaded via-patches with small antennas have been proposed16,17 to enhance radiation efficiency However, these antennas require parameter configuration at the feed point and via-holes The position of the shorting vias or via-patches affects the performance of PIFA tag antennas Resonant frequency tuning is challenging, and fabrication costs can increase considerably Folded patch antennas have been developed on the basis of the PIFA to enhance tag antenna performance and reduce the size of the patch In,18 a miniature folded patch was proposed for designing a passive tag mounted on metal objects The antenna consists of a square patch that is equally separated into two rectangular patches and connected to two ground planes using six thin inductive stubs This structure is fabricated by using an aluminum patch, which decreases the performance of the reading range because of the nature of the adhesive bonding, and the aluminum film on the surface can be easily oxidized.19 Furthermore, the folded structures regularly use additional ground planes or radiating patch layers, which increases the complexity and volume of tag antennas.20,21 Unlike previous antennas, the antenna proposed in22 is robust and does not require additional grounds or radiating patch layers However, the use of two shorting stubs in the middle of the patch to connect the two separated ground planes increases the difficulty in obtaining the resonant frequency In this study, a tag antenna with flexible impedance tuning methods on the metallic plate was developed The proposed antenna is compact, low cost, low profile and simple and does not require shorting vias or additional layers (ground or radiating patch) Furthermore, the proposed antenna can be adjusted easily by tuning the width of the shorting wall, two slits, C-shaped arm, a slot in the middle of the patch, and the position of the loop to achieve conjugate impedance matching with a UCODE 8/8 m chip Antenna performance, including reflection coefficients, gains, the power transmission coefficient, and reading distances of the proposed tag antenna mounted on the metal plate of 220 × 220 mm2, was NGUYEN ET AL investigated All simulations were performed using Ansoft HFSS software This paper is organized into five main sections Section II introduces the configuration of the proposed antenna Section III discusses the design procedure and current analysis Section IV describes the effects on parameters Section V presents the experiment results and compares the performance of the proposed antenna with those in previous studies | ANTENNA DESIGN AND OPTIMIZATION A compact shorted C-shaped tag antenna on the metallic objects (Figure 1) was proposed and designed at FCC standard frequency bands (902-928 MHz) for North America and Taiwan The tag antenna has a small gap (0.1 mm) and is mounted on a metallic object (220 × 220 mm2) The proposed antenna consists of a C-shaped resonator and a ground plane connected to a small shorting wall and fed by a loop in the middle of the C-shaped resonator The dimensions of the small shorting wall are Sw × mm2 The space between them is supported by a soft foam material (Polyethylene) measuring of 30 × 30 × 2.6 mm3, a dielectric constant of 1.03 and a loss tangent of 0.0001 Two open slits are etched around the shorting wall measuring Wn × 2.2 mm2 The slot and feeding loop are 3.5 × WS mm2 and LC × 0.5 mm2, respectively, and are used to adjust the impedance matching between the proposed antenna and chip They can be easily made by the two FR4 substrates (the top substrate is used to the radiation layer and the other one is a metallic ground plane) with thickness of FIGURE plate Schematic of the proposed antenna on the metallic of 13 NGUYEN ET AL 0.2 mm, dielectric constant εr of 4.3, and loss tangent of 0.025 The microchip used in this design is the UCODE 8/8 m, which has an input impedance of 13 − j191 Ω at 915 MHz, a read sensitivity of −22.9 dBm, and a write sensitivity of −17.8 dBm over the frequency band of 840 to 960 MHz Notably, in this study, test pads TP1 and TP2 were electrically disconnected and therefore could be safely short-circuited to the RF pads (RF1, RF2) in the UCODE 8/8 m These pads of the UCODE chip are particularly described in Figure and Table In Figure 2A, the pads (TP1 and TP2) of chip are a supporting pad for fix In Figure 2B, the feed pads of the antenna are designed a single-slit assembly to make easy to solder in the fabrication In this case, the related increased input capacitance is canceled by using optimize the antenna size Therefore, the tag antenna was designed to match a conjugate input impedance of 13 − j191 Ω of single-slit assembly at the frequency of 915 MHz.23 The chip was soldered to the middle of the short side of the rectangular feeding loop connected to the center of the C-shaped radiator The optimized design parameters of the proposed antenna (listed in Table 2) were simulated using HFSS software version 19.3.24 | DESIGN PROCEDURE A ND CURRENT ANALYSIS To obtain an optimal tag antenna design, the design procedure used HFSS, and the characteristics of the input impedance of the proposed antenna were investigated To validate our design, an antenna prototype was also fabricated (Figure 3) Because the frequency-dependent complex impedance induced by a tag chip substantially affects the performance of an RFID tag, the input impedance of the chip was determined before RFID tag design FIGURE First, the method described in25 was used to determine the threshold power sensitivity, which was approximately −22.9 dBm at 915 MHz Second, the threshold power sensitivity was adjusted to 915 MHz Figure 4A depicts that a balun probe was connected to a vector network analyzer (VNA) set up from 800 to 1000 MHz through a coaxial cable of 50 Ω to measure the input impedance of the chip by observing the pointer position in the Smith chart circle Furthermore, the balun probe was calibrated by using the open, short, and load before starting this measurement Third, the values of the chip resistance and reactance were measured and are presented in Figure 4B Finally, the tag antenna was executed by following design procedures The design required a conjugate impedance match between the tag antenna and the UCODE 8/8 m chip, which has a ZA value of 13 + j191 Ω at 915 MHz The design method entailed the four stages described in the following: Stage 1: The C-shaped patch is connected to the loop in the middle of the antenna, which does not have a shorting wall, slits, and a slot, in the early stage of design Figure 5A indicates that the resonant frequency of the antenna is higher than that required; the tag antenna achieves a reactance of j191 Ω at 1220 MHz because the high current density is only concentrated in the middle of the C-shaped patch and loop, as depicted in Figure 5B The resonance frequency is shifted downward by increasing the current path TABLE Pads description of the bare die Symbol Description TP1 Test Pad RF1 Antenna connector TP2 Test Pad RF2 Antenna connector Pads of the UCODE 8/8 m chip: A, standard assembly; B, single-slit assembly of 13 NGUYEN ET AL Para Dim [mm] Para Wm 220 W3 Lm 220 Wa La Para Dim (mm) 8.5 Wn 0.2 WS 0.2 Ln 2.2 30 LS 3.5 Sw 3.35 30 WC 0.5 H W1 LC 13.5 W2 g1 2.5 FIGURE Dim (mm) T A B L E Optimized antenna design parameters Structure of the fabricated antenna Stage 2: The shorting wall is now studied to increase the current density distribution or the current path of the antenna, which decreases the resonant frequency; the shorting wall is used to short the top patch and ground plane Figure 6B displays a high density in the middle of the C-shaped patch and loop and an extended current path, which distributes strongly around the shorting wall Therefore, the resonance frequency is reduced from 1220 MHz to 931.5 MHz (see Figure 6A) Stage 3: To match the impedance of the chip, the resonance frequency of the tag antenna is shifted down at the desired frequency A slot is made in the middle of the C-shaped patch The existence of the slot causes the current distribution of the C-shaped patch to focus on the contour of the edge of the Cshaped left arm, as displayed in Figure 7B Therefore, this method reduces the resonant frequency of the tag to 920.5 MHz (Figure 7A) Stage 4: Finally, the two slits are etched on the top patch around the shorting wall, which makes the current path longer than the case without the slits, as depicted in Figure 8B Therefore, the resonant frequency shifts from 920.5 to 915 MHz; the result is excellent conjugate impedance agreement between the proposed antenna and the chip (Figure 8A) Furthermore, changing the F I G U R E Measured chip impedance vs frequency at the threshold power: A, Balun probe, calibration kit, and B, Cartesian coordinates width of two slits slowly affects the frequency at a rate of MHz per 0.3 mm In summary, Figure 8B displays the surface current distribution on the proposed antenna mounted on the 220 × 220 mm metallic plate and a resonant current flow on the radiating plate at 915 MHz Almost all the current is concentrated on the left arm of the C-shaped patch, shorting wall, two slits, slot, and the contour of the loop, which suggests these are useful for tuning the resonant frequency of the tag antenna NGUYEN ET AL F I G U R E A, Resistance and reactance for the case not having slits, a slot, and shorting wall; B, surface current distribution of the patch of 13 F I G U R E A, Resistance and reactance for the case having a shorting wall but not a slot and slits; B, surface current distribution of the patch | PARAMETER STUDY In this section, the study of fundamental antenna properties, such as the input impedance, reflection coefficient, power transmission coefficient, and gain, which was undertaken to investigate the effect of key parameters on the performance of the proposed antenna, is explained The key parameters include the left arm size of the Cshaped patch (W2), width of the shorting wall (Sw), size of the two slits (Wn) and slot (Ws), and vertical length of the loop (Lc) In all simulation cases, the tag was attached at the center of the metallic plate measuring 220 × 220 mm2 with a small gap of 0.1 mm The goal of this study was to design a flexible antenna structure that can easily match the input impedance of the UCODE 8/8 m chip by changing multiple parameters The effects of the shorting wall were first studied (Figure 9) The reflection coefficient is depicted in Figure 9B; the resonance frequency of the tag is sensitive to the width of the shorting wall The resonance frequency increased at a rate of MHz with an increase of 0.8 mm in Sw because the tag antenna became resistive and reactive when the length of shorting wall decreased (Figure 9A) The input impedance bandwidth for a dB reflection coefficient was 1.8%, ranging from 905 to 923 MHz Additionally, the performance of the tag antenna was 95% of the power transmission coefficient at the resonance frequency as illustrated in Figure 9c The effects of the left arm of the C-shaped (W2) were then evaluated As illustrated in Figure 10A, the resistive and reactive characteristics largely increased every mm as the left arm size decreased in W2, which shifted the resonance frequency downward quickly, as depicted in Figure 10B, whereas the power transmission coefficient was almost unchanged, as depicted in Figure 10c The effects of the vertical length of the loop were then studied As illustrated in Figure 11A, the resonance frequency decreased at a rate of MHz as the vertical length of the loop (LC) increased from 12.5 mm to 14.5 mm, whereas the impedance bandwidth at dB did not change Notably, the performance of the tag degraded in this scenario The power transmission coefficient decreased from 96.4% to 88% with an increment of mm in LC (Figure 11B) Next, the effects of the slot (WS) were evaluated (Figure 12) The results were similar to those of studies that analyzed cases of changing the loop and of 13 F I G U R E A, Resistance and reactance for the case having a shorting wall and slot but without slits; B, surface current distribution of the patch increasing the effect of WS on tag resistance and reactance, and that decreases the resonant frequency (Figure 12A and B) Furthermore, the power transmission coefficient also slightly decreased as the width of the slot increased by 0.8 mm Finally, the effects of changing the Wn of the two slits were analyzed (Figure 13) Figure 13A indicates that the resistance and reactance increased slowly when the width of slits was varied from 0.2 to 0.8 mm Therefore, the resonant frequency of the tag only slightly decreased at the rate of MHz per 0.3 mm Figure 13C,D displays the performance of the tag in terms of PTC and reveals that the gain with 0.3 dB was unchanged in this case The simulation results indicated that this slow shifting was an excellent method to accurately adjust the resonance frequency of the tag (Figure 13B) | EXPERIMENT AND DISC USS I ON The proposed UHF RFID tag antenna was fabricated by using two FR4 substrates (thickness: 0.2 mm, dielectric NGUYEN ET AL F I G U R E A, Resistance and reactance for the case having a shorting wall, slits, and slot; B, surface current distribution of the patch constant εr = 4.3, and loss tangent δ = 0.025), measuring 30 × 30 × 0.2 mm3 and one measuring 30 × 2.6 × 0.2 mm3 for the C-shaped patch and ground plane and the side of the tag, respectively The space between the top and bottom layers was supported by a soft foam material (εr = 1.03), as displayed in Figure The tag antenna was designed for a UCODE 8/8 m chip, which had an input impedance of 13 − j191 Ω and a power sensitivity of −22.9 dBm at 915 MHz The input impedance measurement of the tag was implemented using the VNA, which was connected to the balun probe through the coaxial cable with a resistance of 50 Ω Notably, the balun probe was calibrated through open, short, and loads before performing this measurement with reference to Figure 4A Therefore, Figure 14 displays the comparison of the measured and simulated input impedance of the tag antenna with the UCODE 8/8 m chip as the reference The input impedance of the tag antenna in measurement and simulation were obtained at 13 + j215 Ω and 11 + j219 Ω, respectively, and slightly shifted compared with the chip at 915 MHz To verify a matching agreement between input impedance of the chip and the tag antenna, the performance characteristic parameters, including the reflection coefficient or return loss and of 13 NGUYEN ET AL (A) (B) (C) F I G U R E Effect of changing Sw of the shorting wall: A, Resistance and reactance; B, reflection coefficient; C, power transmission coefficient F I G U R E Effect of changing W2 of the C-shaped left arm: A, Resistance and reactance; B, reflection coefficient; C, power transmission coefficient power transmission coefficient, were first implemented In,26 a power wave reflection coefficient Γ is expressed as follows: Z T −Z *A , 0≤jΓj≤1 , ZT + ZA Return Loss ðdBÞ = −20log jΓj Γ= where ZT = RT + jXT is the complex chip impedance ZA = RA + jXA is the complex antenna impedance The power delivered to the chip is expressed as follows: ð1Þ Ptag − chip = − jΓj2 Ptag − ant , ð2Þ where Ptag - ant is the power received by the tag antenna 8 of 13 NGUYEN ET AL (A) (A) (B) (B) (C) F I G U R E 1 Effects of changing Lc of the loop: A, reflection coefficient; B, power transmission coefficient The power transmission coefficient can be expressed as follows: Ptag − chip = − j Γj Ptag − ant 4RA RT , 0≤τ≤1 = ðRA + RT Þ2 + ðX A + X T Þ2 τ= ð3Þ The reflection coefficient and PTC were then calculated by replacing the measured results of the resistance and reactance into Equations (1) and (3), as depicted in Figure 15, which illustrates the reflection coefficient between the simulation and measurement A good match occurred between the input impedance of the tag antenna and the chip at the resonance frequency However, the 3-dB bandwidth of the measured result is larger than the simulated result This discrepancy was caused by the fabrication tolerance in the etching process and cable influence in the measurement procedure, which are problems also identified in F I G U R E Effects of changing WS of the slot: A, Resistance and reactance; B, reflection coefficient; C, power transmission coefficient other studies.25,27 Moreover, the measured PTC values were obtained from 60% to 91% at the operation frequency band of FCC (902-928 MHz) for North America and Taiwan, meaning that the impedance matching between the tag antenna and the chip was acceptable (Figure 15) Another crucial parameter that can be used to evaluate the performance of the tag antenna is the reading of 13 NGUYEN ET AL (A) (B) (C) (D) FIGURE 13 Effects of changing Wn of the two slits: A, Resistance and reactance; C, power transmission coefficient; D, antenna gain F I G U R E Measured and simulated input impedance of the proposed antenna vs the chip distance or the read range The maximum reading distance for a radio power link was obtained when Ptag-chip was equal to the threshold power of the microchip, Ptagthreshold, which is the minimum threshold power to activate the microchip on the RFID tag26: F I G U R E Measured and simulated reflection coefficient of the proposed antenna R= where λ rPffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi reader-tx Greader-ant Gtag-ant τ , 4π Ptag-threshold ð4Þ 10 of 13 F I G U R E Measurement setup of the RFID tag antenna for reading range inside the anechoic chamber F I G U R E Measurement setup of the RFID tag antenna for reading the range outside the free space NGUYEN ET AL Preader-tx and Greader-ant are the power and gain of the reader antenna, respectively, Gtag-ant is the gain of the tag antenna, and Ptag-threshold is the minimum threshold power necessary to provide sufficient power to the chip To verify the tag performance, Equation (4) was used to calculate the reading distance The fabricated tag antenna attached to the metallic plane was measured inside the anechoic chamber with a measurement system according to the method described in.25,28 Figures 16 and 17 display the measurement of the tag antenna inside the anechoic chamber and outside the free space, respectively The RFID measurement system included a computer, a reader controller module (Favite FS-GM-201), a reader antenna, which has a circular polarization, and the proposed antenna Figure 18 depicts the angular sensitivity patterns of the tag in the yz and xz planes To obtain the angular sensitivity patterns of the tag, the measurement system was set up to rotate the tag antenna around the fixed axis in the yz and xz planes from 0 to 360 with 15 increments at 915 MHz, as depicted in Figure 18A and B, respectively The proposed antenna exhibited superior input power sensitive values in the yz plane compared with the xz plane at 915 MHz Figure 19A displays that the maximum readable distance was achieved at θ = 0 with a value of 6.4 m when the tag antenna was placed on the yz plane However, the maximum reading range was obtained with a value of 5.1 m if the tag antenna was placed in the xz plane (Figure 19B) An explanation for this phenomenon is that a slight misalignment occurs between the reader and the tag antenna, which is unavoidable during the measurement process Table displays a comparison between the proposed antenna and previously studied antennas mounted on a metallic plate In,18,22 for the tag antennas, shorting stubs were used to connect the top patch to ground layers to decrease the resonant frequency By contrast, the F I G U R E Angular sensitivity patterns of the proposed tag antenna at 915 MHz in A, yz and B, xz planes 11 of 13 NGUYEN ET AL F I G U R E Measured reading range of the proposed tag antenna at 915 MHz in A, yz and B, xz planes TABLE Comparison of the proposed antenna with other tag antennas attached on metal EIRP (W) Chip threshold power (dBm) Size of Tag (mm3) Max read range (m) This work −22.9 30 × 30 × 6.4 22 −17.8 38 × 38 × 1.6 5.3 20 −20 23 × 7.5 × 3.2 5.0 21 −20 25 × 25 × 3.2 11.9 18 3.28 −20 40 × 40 × 1.6 5.0 27 −18 55 × 41.5 × 6.1 28 −18 120 × 60 × 1.9 10 17 −15 26 × 14 × 2.4 5.5 14 0.4 −18 68 × 30 × 3.3 antenna structure in20 includes two layers of the patch that were shorted to the ground layer through two shorting stubs In essence, the antennas in these studies were developed on three layers and require more shorting stubs to tune the impedance match Therefore, the fabricating cost and complexity level were increased considerably, despite the smaller size of the tag antenna Furthermore, the achieved maximum reading ranges were lower than that of the proposed antenna in this paper Similarly, the achievable reading distance in21 was higher than that of our antenna structure However, the tag antenna was implemented on four layers with two layers for the top patch and the other two layers for the ground plane The antennas in14,27 were larger and achieved lower reading ranges than those in our design By contrast,28 the maximum reading range of the proposed antenna was approximately 1.5 times shorter, but the final size was five times smaller In addition, the effect on back-mounted metal was also less than in our study because of the size of the metal In,17 the antenna was considerably small, but the maximum readable range was only 5.5 m, and the minimum input power of chip was higher Therefore, the proposed tag antenna not only was constructed using simple fabrication mechanisms but also exhibited the lowest minimum input power of the chip compared with previously reported designs Furthermore, the fabrication of the tag antenna was low cost and less complex and thus is suitable for applications that require a compact antenna | CONCLUSION A tag antenna with flexible tuning methods was presented and experimentally verified In this proposed antenna, impedance matching can be easily achieved by adjusting the width of the shorting wall, two open slits, a slot, and the vertical length of the loop Moreover, the tag antenna configuration was inexpensive and easily fabricated by using the FR4 substrate The low-profile design (0.092λ0 × 0.092λ0 × 0.0092λ0) of this antenna satisfies the requirements of a compact antenna The tag antenna achieved a maximum reading range of 6.4 m when attached to the metal plate measuring 220 × 220 mm2 12 of 13 A C K N O WL E D G M E N T This manuscript was edited by Wallace Academic Editing ORCID Chien-Hung Chen https://orcid.org/0000-0003-45141504 Hua-Ming Chen https://orcid.org/0000-0002-8051-0267 R EF E RE N C E S Chen CH, Huang ST Low-profile CP RFID hard tag antenna with short-circuited microstrip-fed line mounted on metallic plane Int J RF Microwave Comput-Aid Eng 2018;28:e21504 Bhaskar S, Singh AK Linearly tapered meander line cross dipole circularly polarized antenna for UHF RFID tag applications Int J RF Microwave Comput-Aid Eng 2019;29:e21563 Sallam MO, Soliman EA, Vandenbosch GA, De Raedt W Novel electrically small meander line RFID tag antenna Int J RF Microwave Comput-Aid Eng 2013;23:639-645 Amato F, Hemour S The Harmonic Tunneling Tag: a dualband approach to backscattering communications Paper presented at: IEEE International Conference on RFID Technology and Applications (RFID-TA), Pisa, Italy 2019: 244–247 Bansal A, Sharma S, Khanna R Platform tolerant dual-band UHF-RFID tag antenna with enhanced read range using artificial magnetic conductor structures Int J RF Microwave Comput-Aid Eng 2020;30:e22065 Kim D, Yeo J Dual-band long-range passive RFID tag antenna using an AMC ground plane IEEE Transac Antennas Propag 2012;60:2620-2626 Kim D, Yeo J Low-profile RFID tag antenna using compact AMC substrate for metallic objects IEEE Antenna Wireless Propag Lett 2008;7:718-720 Kim D, Yeo J, Ick CJ Low-profile platform-tolerant RFID tag with artificial magnetic conductor (AMC) Microwave Opt Technol Lett 2008;50:2292-2294 Chen SL, Lin KH A slim RFID tag antenna design for metallic object applications IEEE Antennas Wireless Propag Lett 2008; 7:729-732 10 Lopez-Soriano S, Parron J Design of a small-size, low-profile, and low-cost normal-mode helical antenna for UHF RFID wristbands IEEE Antennas Wireless Propag Lett 2017;16:2074-2077 11 Marrocco G The art of UHF RFID antenna design: impedancematching and size-reduction techniques IEEE Antennas Propag Mag 2008;50:66-79 12 Loo CH, Elmahgoub K, Yang F, et al Chip impedance matching for UHF RFID tag antenna design Prog Electromag Res 2008;81:359-370 13 Ukkonen L, Sydänheimo L Impedance matching considerations for passive UHF RFID tags Paper presented at: 2009 Asia Pacific Microwave Conference, Singapore, Singapore, 2009:2367–2370 14 Lin KH, Chen SL, Mittra R A looped-bowtie RFID tag antenna design for metallic objects IEEE Transac Antennas Propag 2012;61:499-505 15 Chen SL A miniature RFID tag antenna design for metallic objects application IEEE Antennas Wireless Propag Lett 2009; 8:1043-1045 NGUYEN ET AL 16 Chiu CY, Shum KM, Chan CH A tunable via-patch loaded PIFA with size reduction IEEE Transac Antennas Propag 2007;55:65-71 17 Zhang J, Long Y A novel metal-mountable electrically small antenna for RFID tag applications with practical guidelines for the antenna design IEEE Transac Antennas Propag 2014;62: 5820-5829 18 Ng WH, Lim EH, Bong FL, Chung BK Folded patch antenna with tunable inductive slots and stubs for UHF tag design IEEE Transac Antennas Propag 2018;66:2799-2806 19 An B, Wu Y, Cai X, Wu F Reliability of RFID tag inlay assembled by anisotropic conductive adhesive Paper presented at: 2nd Electronics System-Integration Technology Conference, Greenwich, UK, 2008: 1203–1208 20 Thirappa K, Lim EH, Bong FL, Chung BK Compact foldedpatch with orthogonal tuning slots for on-metal tag design IEEE Transac Antenna Propag 2019;67:5833-5842 21 Ng WH, Lim EH, Bong FL, Chung BK Compact planar inverted-S antenna with embedded tuning arm for on-metal UHF RFID tag design IEEE Transac Antennas Propag 2019; 67:4247-4252 22 Lee SR, Ng WH, Lim EH, Bong FL, Chung BK Compact magnetic loop antenna for omnidirectional on-metal UHF tag design IEEE Transac Antennas Propag 2020;68:765-772 23 Available at: www.nxp.com/docs/en/data-sheet/SL3S1205-15DS.pdf 24 Available at: www.ansys.com/products/electronics/ansys-hfss 25 Chen H, Yeh S, Lin Y, Pan S, Chang S High chip reactance matching for ultra-high-frequency radio frequency identification tag antenna design IET Microwaves Antennas Propag 2012;6:577-582 26 Zhi NC Antenna for portable devices John Wiley & Sons; 2007 27 Li H, Zhu J, Yu Y Compact single-layer RFID tag antenna tolerant to background materials IEEE Access 2017;5:2107021079 28 Lin YF, Chang MJ, Chen HM, Lai BY Gain enhancement of ground radiation antenna for RFID tag mounted on metallic plane IEEE Transac Antennas Propag 2016;64:1193-1200 AUTHOR BIOGRAPHIES Minh-Tan Nguyen received the BS degree in Physics and MS degree in Electronics and Telecommunication Engineering from Vietnam National University Ho Chi Minh City in 2007, and 2013, respectively Under the guidance of his Advisor, he has been awarded the Best Student Paper Award in the 2020 IEEE International Workshop on Electromagnetics: Applications and Student Innovation Competition (IEEE IWEM 2020) He is currently pursuing the PhD degree in Electronic Engineering with Institute of Photonics Engineering, National Kaohsiung University of Science and Technology His main research 13 of 13 NGUYEN ET AL interests include antenna design for RFID Tags and MIMO antennas Yi-Fang Lin received the BS degree in physics from National Tsing Hua University, Hsinchu, Taiwan in 1993, both the MS degree in Institute of electro-optical engineering and the PhD degree in electrical engineering, from National Sun Yat-Sen University, Kaohsiung, Taiwan, in 1995, and 1998, respectively Since 2000 she has been with the Institute of Photonics Engineering at National Kaohsiung University of Science and Technology, Taiwan, where she became a Professor in 2013 Her current research interests include microstrip antennas, dielectric resonator antennas and small antennas design Chun-Hsien Chang received the BS degree of Department of Communication Engineering from National Penghu University of Science and Technology in 2018 and the MS degree from Institute of Photonics Engineering at National Kaohsiung University of Science and Technology in 2021 His research interests include RFID antennas, beamforming antennas and MIMO antennas Chien-Hung Chen received the BS degree in Electronic Engineering from ROC Air Force Academy, Taiwan in 2004, the MS degree in Institute of Communication & Photonics and the PhD degree in Electrical Engineering, from National Kaohsiung University of Science and Technology, Taiwan in 2007 and 2012, respectively He is a visiting professor of University of Florida at 2014 His research interests include avionics antennas and microwave system design Prof Chen is an IEEE AP-S Tainan Chapter vice chairman since 2017 Now he is an associate professor and a department chairman of Avionics at ROC Air Force Academy Hua-Ming Chen (M'98-SM'06) received the BS degree in physics from National Tsing Hua University, Hsinchu, Taiwan, the MS degree in Institute of Electro-Optics from National Chiao Tung University, Hsinchu, Taiwan, and the PhD degree in electrical engineering from National Sun Yat-Sen University, Kaohsiung, Taiwan, in 1983, 1987, and 1996, respectively Since 1988 he has been with the Institute of Photonics and Communications at National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan, where he became a Professor in 2001 He also served as Director of Institute of Photonics and Communications at the same university from 2005 to 2008 He has published more than 110 journal and conference papers and takes out 20 patents on antenna design Several of his antenna designs have been licensed to industry for production His current research interests include antennas for smart connected devices, dielectric resonator antennas, RFID antennas and microwave filter design He was elected as a President of the Institute of Antennas Engineers of Taiwan (IAET) in 2010-2012 He was also elected as Chair of IEEE AP-S Tainan Chapter in 2009-2010 and has received IEEE 2011 Best Chapter Award He served as Trustees of IEEE Tainan Section (2010-2011) and Chinese Microwave Association (2009-2011) He also served as a Publications Committee Chair of ISAP 2014, International Technical Program Committee member of IEEE AEM2C 2010 and IEEE iWEM 2011 in Taiwan How to cite this article: Nguyen M-T, Lin Y-F, Chang C-H, Chen C-H, Chen H-M Compact shorted C-shaped patch antenna for ultrahigh frequency radio frequency identification tags mounted on a metallic plate Int J RF Microw Comput Aided Eng 2021;e22595 https://doi.org/ 10.1002/mmce.22595 ... 13 and are not cost effective Therefore, these antennas are impractical for applications that require a compact antenna To reduce the profile of the tag antenna, a planar inverted-F antenna (PIFA)... PIFA tag antennas Resonant frequency tuning is challenging, and fabrication costs can increase considerably Folded patch antennas have been developed on the basis of the PIFA to enhance tag antenna. .. Taiwan How to cite this article: Nguyen M-T, Lin Y-F, Chang C- H, Chen C- H, Chen H-M Compact shorted C- shaped patch antenna for ultrahigh frequency radio frequency identification tags mounted on