# Design of RFID Tag Antenna for Logistics Applications in the Renewable Energy Sector

Y. Esshaimi, F. Aytouna, J. Zbitou, Mohammed El Gibari, R. Er-Rebyiy, A. Errkik

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Y. Esshaimi, F. Aytouna, J. Zbitou, Mohammed El Gibari, R. Er-Rebyiy, et al., Design of RFID Tag Antenna for Logistics Applications in the Renewable Energy Sector. International Conference on Functional Materials and Renewable Energies: COFMER'05 5th Edition, Apr 2025, Tanger, Morocco. pp.05008, 10.1051/epjconf/202532605008. [hal-05233969](https://HAL Id: hal-05233969)

Submitted on 6 Nov 2025

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# Design of RFID Tag Antenna for Logistics Applications in the Renewable Energy Sector

Y. Esshaimi<fnref n="1" />*, F. Aytouna<fnref n="1" />,<fnref n="2" />, J. Zbitou<fnref n="1" />,<fnref n="2" />, M. El Gibari<fnref n="3" />, R. Er-rebyiy<fnref n="4" /> and A. Errkik<fnref n="5" />

**Abstract.** In the era of Green IoT, where logistical efficiency is a critical success factor, the integration of RFID technology in strategic sectors such as wind turbines and solar power plants enhances automation and enhancing clean energy productivity. This paper presents the design and optimization of a miniaturized, flexible passive UHF RFID tag antenna with a compact size of 54 × 54 mm<fnref n="2" />. The antenna is implemented on an eco-friendly HP photopaper substrate, characterized by a permittivity of 3.3, a loss tangent of 0.04, and a thickness of 0.25 mm. This proposed tag antenna is specifically matched to an Impinj Monza 1a microchip, which has an impedance of Zchip = 33 - j112 Ω at 915 MHz and a sensitivity of -9 dBm. The antenna's performance is evaluated based on key parameters. Simulation results demonstrate a reflection coefficient of -31 dB at 915 MHz, a positive gain of approximately 0.39 dBi, and a read range equal to 2.8 meters. This innovative solution is particularly suited for RFID applications requiring compact, flexible, and efficient devices for real-time identification, tracking, and operational automation.

**Keywords** Green IoT, RFID technology, miniaturized and flexible, passive RFID UHF tag, automation.

## 1. Introduction

Nowadays, the transition to renewable energy is experiencing unprecedented growth, driven by the need to reduce carbon emissions and meet the rising demand for clean and sustainable energy. However, technical challenges persist, particularly the need to accelerate production rates. It is therefore essential to integrate innovative technologies capable of optimizing and automating processes.

Among these innovations, Radio Frequency Identification (RFID) technology stands out as a strategic tool for optimizing equipment management and monitoring. By enabling contactless identification, real-time tracking, and automated asset management, RFID enhances supply chain traceability, performance monitoring, and preventive maintenance of infrastructures such as solar panels, wind turbines, and energy storage systems [1].

An RFID system typically consists of a tag attached to an object and a reader, which serves two main functions: wirelessly supplying power to the tag and retrieving the data stored in its embedded microchip. These systems are generally classified into different categories based on criteria such as operating frequency, power source, and communication protocol, as outlined in reference [2].

In this study, we focus on passive RFID tags operating in the UHF band due to several advantages, including long reading range, omnidirectional radiation pattern, low cost, and compact size, which meet the

requirements of the targeted applications. It is worth noting that the UHF band allocated for RFID tags varies across regions, covering a frequency range from 860 to 960 MHz [3]. The different frequency bands used in various regions are presented in reference [4].

## 1. Tag antenna design technology

In the context of emerging Green IoT applications, this research addresses several major challenges related to the next-generation RFID tags, including antenna miniaturization, the use of flexible and eco-friendly substrates, and the development of high-performance structures that are compatible with low-cost manufacturing techniques such as inkjet and screen printing.

One of the primary tasks in RFID antenna design is to ensure efficient impedance matching between the antenna and the RFID chip [5]. Due to the capacitive and complex nature of typical RFID chip impedances, special attention must be given to antenna design to ensure optimal conjugate matching [6]. This minimizes the power reflection coefficient and, consequently, maximizes power transfer to the RFID chip. First, the power reflection coefficient is defined as [6]:

$$ \Gamma = \frac{Z_a - Z_c^*}{Z_a + Z_c^*} \qquad (1) $$

$$ Z_a \text{ is the antenna impedance: } Z_a = R_a + j X_a \qquad (2) $$

$$ Z_c \text{ is the impedance of the chip: } Z_c = R_c + j X_c \qquad (3) $$

<footnote n="1">¹ LABTIC, ENSA of Tangier, Abdelmalek Essaadi University, Tangier, Morocco</footnote>

<footnote n="2">² ENSA of Tetouan, Abdelmalek Essaadi University, Tetouan, Morocco</footnote>

<footnote n="3">³ Institute of Electronics and Digital Technologies (IETR), UMR CNRS 6164, Nantes, France</footnote>

<footnote n="4">⁴ EMSI, Marrakech, Morocco</footnote>

<footnote n="5">⁵ FST of Settat, Morocco</footnote>

<footnote>* Corresponding author: E-mail address: yassmine.esshaimi@etu.uae.ac.ma (Y. ESSHAIMI)</footnote>
Various methods for achieving impedance matching have been introduced in prior studies, including T-matching networks, inductive feed loops, short-circuited open-ended microstrip lines, proximity coupling, and open stub feeding techniques [8–15]. In the present work, impedance matching with the selected RFID chip is accomplished using an inductively coupled loop configuration, which incorporates a wide gap along with T-shaped stubs.

## 2. Design procedure and result discussion

A compact RFID tag antenna operating at 915 MHz is introduced, utilizing a circular loop configuration. The design incorporates a half-wavelength (λ/2) perimeter ring with a wide gap, functioning as the primary radiating component, while a loop element linked to the RFID chip ensures power feeding. Numerical simulations were carried out using CST Microwave Studio to assess the performance of the proposed structure. The substrate for the tag is made of HP paper, with a relative permittivity of 3.3, a loss tangent of 0.04, and a thickness of 0.25 mm, while copper is employed as the conductive material element. The overall geometry of the antenna is depicted in Fig. 1, with specific dimensional parameters listed in Table 1.

<figure><img src="image_2.png" /><figcaption>Fig 1: Structure of the developed RFID tag antenna</figcaption></figure>

<table><caption>Table 1: Dimensional parameters of the antenna after optimization.</caption><thead><tr><td>Parameter</td><td>Value (mm)</td></tr></thead><tbody><tr><td>c</td><td>1.18 (dimension of chip)</td></tr><tr><td>Rout</td><td>27</td></tr><tr><td>Rin</td><td>25</td></tr><tr><td>r1</td><td>22</td></tr><tr><td>r2</td><td>20</td></tr><tr><td>w</td><td>1.5</td></tr><tr><td>V</td><td>15</td></tr><tr><td>g</td><td>9.75</td></tr><tr><td>d</td><td>3</td></tr></tbody></table>

To achieve good antenna performance, it is necessary to optimize the most influential structural parameters. Our studies show that each parameter differently affects the reflection coefficient, the input impedance, and the gain. In this section, we analyze these effects.

The first investigation concerns width of the radiating Loop Gap (g). As presented in Fig.2

The gap width (g) is a determining factor for the antenna's resonant frequency. Increasing g shifts the resonant frequency to higher values, while decreasing g moves it to lower frequencies. According to the optimization, setting g to 9.75 mm can achieve a desired resonance at 915 MHz.

<figure><img src="image_3.png" /><figcaption>Fig 2: The reflection coefficient simulation S11 with optimized parameter (g)</figcaption></figure>

The second study concerns the distance (d) between the radiating ring and the coupled feeding loop, a crucial parameter in RFID antenna design, as it represents the coupling effect between these two parts of the antenna. The optimization of this parameter has shown that increasing this distance (d) reduces inductive coupling, which leads to a decrease in bandwidth and impedance mismatch between the antenna and the chip used in this study. This directly affects the RFID tag's read range. In this work, we found that a distance of 3 mm between the radiating ring and the coupled feeding loop improves the antenna's performance.

Other parameters of interest in the optimization include the length of the two vertical stubs, as we have observed that they have a significant impact on the adaptation of S11 to the resonant frequency. This leads to a better impedance matching between the antenna's input impedance and that of the chip, thereby improving the overall performance of the RFID tag.

<figure><img src="image_4.png" /><figcaption>Fig 3: simulation of the reflection coefficient S11 with optimized of the length parameter of the vertical stubs</figcaption></figure>

Figure 3 presents the simulation of the optimization of the length parameters of the vertical stubs; one located on the left and the other on the right inside the feeding loop. It is observed that a precise adjustment of these lengths can improve the S11 parameter without altering the resonant frequency, which helps match the antenna's impedance to the conjugate impedance of the Impinj Monza 1a chip, which has an impedance according to the datasheet of $Z_c = 33 - j112 \Omega$ [7]. In practice, based on optimizations performed using CST, the two T-shaped stubs should be
symmetrical, with a 10 mm spacing separating them, which is sufficient for impedance matching. The optimized dimensions for the stubs are 15 mm in length and 1.5 mm in width.

After refining the design through optimization and parameter selection, the final performance results of the developed antenna are detailed in this section. Figure 4 illustrates the simulated real and imaginary parts of the input impedance of the designed tag antenna as a function of frequency. As observed, the input impedance at the target frequency of 915 MHz is $Z_a=32.9+j112.3 \Omega$, which closely matches the complex conjugate of the RFID chip's impedance $Z_c=33-j112 \Omega$. This indicates a good matching of the antenna at the resonance frequency, thanks to the effective impedance matching techniques used in this work.

<figure><img src="image_5.png" /><figcaption>Fig 4: simulation input impedance of the developed antenna.</figcaption></figure>

Figure 5 shows the reflection coefficient of the developed tag antenna structure as a function of the resonance frequency. The simulated S11 reaches -31 dB well below the -10 dB threshold, indicating efficient impedance matching for our tag antenna.

As for the bandwidth, it is approximately 16.26 MHz, which closely approaches the coverage of the UHF RFID band allocated in ITU Region 2 (902–928 MHz), as illustrated in Fig. 6.

<figure><img src="image_6.png" /><figcaption>Fig 5: simulated S11 of the developed RFID tag antenna.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig 6: Bandwidth of the developed RFID tag antenna.</figcaption></figure>

For understanding the behavior of the antenna, the 3D radiation pattern is shown in Figure 7 it can be observed that the RFID tag has a maximum directivity of 1.522 dBi and a gain of 0.3853 dBi at 915 MHz. Furthermore, Figure 8 presents the simulated radiation patterns in both the H-plane and E-plane at the operating frequency. The results indicate that the antenna exhibits an omnidirectional radiation characteristic.

<figure><img src="image_8.png" /><figcaption>Fig 7: 3D Radiation of the developed antenna at 915MHz</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig 8: 2D radiation pattern at 915 MHz. (a) H-plane and (b) E-plane field pattern.</figcaption></figure>

At this point, we introduce a critical parameter for RFID tags, known as the read range. It refers to the distance at which the tag, via the antenna, receives the minimum threshold power required for activation and subsequently backscatters a signal. In other words, it represents the maximum distance at which the reader can detect the tag’s response. This parameter depends on several factors, including the operating frequency, the gains of both the reader and tag antennas, and the chip’s sensitivity (Pth) [12]. The read range is determined using the Friis transmission equation, expressed as follows [13], as well as for a complete explanation of the parameters in this equation, refer to [14].

$$d = \frac{c}{4\pi f} \sqrt{\frac{EIRP.G_{ant} \cdot \tau}{P_{th}}} \quad (4)$$

We use two methods to estimate the read range, one with a MATLAB script and another by exporting of CST data to Excel. The results demonstrate read range about 2.8 m from MATLAB method and 2.75 m from the Excel method, present Fig. 9.
<figure><img src="image_10.png" /><figcaption>Fig 9: Read range of the developed RFID tag antenna.</figcaption></figure>

Table 2. Comparison of the developed antenna with reported designs in the literature in terms of size, resonance frequency, gain, bandwidth, and read range. According to this table, the antenna proposed in this work is smaller in size especially for flexibility requirement of tag and the read range is acceptable.

<table><caption>Table 2: Comparison of the performance of the developed antenna with other designs</caption><thead><tr><th>Ref</th><th>Size (mm²)</th><th>Substrate</th><th>Resonance frequency (MHz)</th><th>Gain (dBi)</th><th>Bandwidth (MHz)</th><th>Read range (m)</th></tr></thead><tbody><tr><td>[2]</td><td>44.1×44.1</td><td>FR4</td><td>915</td><td>-</td><td>913</td><td>-</td></tr><tr><td>[13]</td><td>84.6×28</td><td>HP-Paper</td><td>915</td><td>-0.35</td><td>32.8</td><td>6.2</td></tr><tr><td>[16]</td><td>32×18</td><td>FR-4</td><td>868</td><td>-12.9</td><td>1.94</td><td>1.6</td></tr><tr><td>This work</td><td>54×54</td><td>HP-paper</td><td>915</td><td>0.39</td><td>16.26</td><td>2.8</td></tr></tbody></table>

## Conclusion

This study presents a miniaturized RFID antenna designed to provide an eco-friendly and cost-effective solution for renewable energy equipment. It will facilitate the tracking of essential components, reduce maintenance costs, and improve the efficiency of logistical operations. This paper also examines the effects of the antenna's dimensional parameters on its performance, in order to test and verify the impedance matching techniques used in this design, namely the inductively coupled feeding method and T-shaped stubs.

The simulation results show that the proposed RFID antenna offers a positive gain of 0.39 dBi and a read range of 2.8 meters, suitable for logistical applications requiring a medium read range. The antenna, with its compact size of 54 × 54 mm² and eco-friendly HP photo paper substrate, is cost-effective and simple to manufacture.

The future perspective is to fabricate this structure using the inkjet printing method and validate the simulation results through a reading test with an RFID base station.

Additionally, to enhance the performance of this RFID tag antenna, particularly key aspects such as improving flexibility, increasing gain, or extending bandwidth, we propose improvement avenues for future work. The use of innovative materials with high electrical conductivity could improve gain and thus optimize one of the most critical RFID tag performances: read range.

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