Analysis and Design of a High Gain Multiband Antenna Based on Metamaterials for RFID Applications

. In this research work, the design of a dipole antenna based on metamaterials is proposed, which can be used as a high gain multiband communication device for RFID applications. This antenna is printed on two sides of an Arlon substrate, which has an overall electrical dimension of 0 39 λ 0 × 0 11 λ 0 × 0 0014 λ 0 . The metamaterials are used to obtain a multiband antenna, and their integration technique into the antenna results in a high gain compared to a conventional antenna without any magni ﬁ cation or additional layer. The simulated and measured results show that the proposed antenna can operate at 0.88-0.97 GHz, 2.41-2.48GHz, and 5.77-5.91GHz with a re ﬂ ection coe ﬃ cient of less than − 10dB, which make it well suited for RFID at 860-960 MHz and 2.4GHz/5.8 GHz. All these resonant frequencies show better impedance matching with high gain. The proposed antenna has the advantages of simple design, low pro ﬁ le, easy feeding, low manufacturing cost, and easy integration into the electronic circuit.


Introduction
In recent decades, the rapid development and expansion of advanced wireless technologies such as RFID, GPS, GSM, Bluetooth, WLAN, WiMAX, and 5G NR has led to new requirements for small communication devices that can perform various functions and provide multiple services.In these wireless applications, it is becoming increasingly difficult to integrate multiple antennas into a single device, because having more than one antenna to cover multiple frequencies makes the terminal quite large and leads to mutual coupling when each frequency band is generated by a single antenna.This method not only leaves space for additional components and lowers costs to increase customer interest but also improves communications in operation by reducing weight and avoiding complexity and losses in the coverage network.This challenging task has led antenna designers to look for a multifunctional antenna that can, in particular, cover several frequency bands at the same time, such as RFID at UHF (860-960 MHz) and SHF (2.4/5.8GHz) without interference with coexisting bands.In addition, a multifunctional antenna with low manufacturing cost, easy feeding, light weight, and easy integration into an environment with microwave components is one of the most important requirements in RFID application.However, operating an antenna in multiple bands without inevitable performance degradation is still an important area.This is because the antenna performance, which directly determines the quality of the communication system, rarely remains unchanged with the demand for multiband capabilities.Therefore, various approaches and techniques have been proposed to develop multiband features in a single structure and maintain or improve its performance.These techniques include slots, parasitic elements, differential feeding, frequency selective surfaces (FSS), metamaterials, and stacked patches.Indeed, slots have attracted much attention.In ref [1], a three-band antenna with circular slot technology is proposed for WLAN/WiMAX communication.By using this technique, the antenna has achieved significant impedance matching at all three resonant frequencies.However, it is difficult to achieve the high gain.
In ref [2], a ring-shaped dual-band slot antenna with an integrated filtering network is used to miniaturize the antenna size.Since the size of the antenna is influenced by the slot, the gain/efficiency effect should be considered when designing the antenna.The antenna in ref [3], with an overall size of 100 × 160 × 1 6 mm 3 , achieves a dualband UHF 0.915/2.45GHz RFID reader by bending a metallic conductor spiral with five turns.By combining these elements, the radiation pattern can be set low, especially at 2.45 GHz, although this antenna is very large and does not cover the SHF band.L-shaped slots [4] and starshaped fractal slots [5] are integrated on the radiating patch to increase the number of frequency bands and improve the gain to cover wireless systems.By inserting these slots, the effective length of the antenna is increased, resulting in better impedance matching and consequently a reduction in size.However, this can lead to a deterioration in the performance of the antenna in terms of gain and directivity.Another technique [6][7][8][9][10] has been proposed to obtain a multiband antenna with smaller size, namely, to change the shape of the antenna, which can drastically reduce the amplitude of the current distribution in the radiator near the ground to suppress unbalanced current.Although these antennas have the advantage of compact size, the gain of the antennas remains very low.This trade-off relationship between antenna performance and size can be reduced by using multilayer substrates made of different materials.In [11], a three-port triband antenna with slot-coupled feed technique on three-layer substrates for radio frequency identification (RFID) is presented.Similarly, multiband patch antennas with feed technique implemented on twolayer substrates [12][13][14] and three-layer substrates [15] are proposed for wireless applications.An increase in bandwidth could be achieved together with a gain.In addition, these antennas can be used to generate circularly polarized radiation.However, due to the multilayer substrate and the multiple feed technique, the fabrication of this type of structure is complicated and very large.In addition, multiple feeding techniques and extra space are usually required to develop and place the multilayer substrates.To overcome this problem, several research papers have proposed a technique that combines two structures of the same shape and different sizes, with each radiating element supporting one or the other operating band.The antennas in refs [16][17][18][19][20] achieve two-band coverage by combining moxon and quasi-Yagi, stacked patches, dipoles, four dipoles, or patch and dipole array.These structures are simple, can be easily integrated into other RF microwave circuits, and provide better gain than conventional antenna radiators because antenna's radiated power can be increased by changing the radiating structure.However, only a dual band can be achieved that can cover only one wireless application, so an extra space is needed to add a new radiating element.This technique could be improved by combining the parasitic elements [21][22][23] with a modified antenna.Although these structures are useful for WLAN/WiMAX with a sim-ple and compact size, they do not cover the UHF RFID band.For all these reasons, several works have addressed the use of metamaterials (MTM) to enhance the performance of the antenna and achieve multiband capability, as metamaterials produce more additional resonant modes when the input impedance of the antenna is changed.By loading metamaterial elements [24][25][26][27] with a radiating patch, different resonant modes can be achieved near the main frequency served by the radiating patch because coupling has occurred between the radiating patch and these elements.For all these structures, the maximum achievable gain is of the order of 2-6 dB in the UHF and SHF bands, which is not suitable for RFID application because the antenna, which has low performance in terms of gain and directivity, may cause tag detection errors or losses in the supply network in other applications, thus limiting the range of applications.There are numerous techniques based on metamaterials that can be employed above [28], or inside the radiating element [29][30][31].However, only a single band has been successfully achieved around 2.4 GHz, with a maximum gain of 6 dB, at the expense of increased size.The problem is that there is a trade-off between space and performance constraints.To overcome this problem, this paper investigates the design of a dipole antenna based on metamaterials that can perform multiple functions effectively and simultaneously, with the aim of achieving multiband characteristics along with high gain.This antenna is not only suitable for multiband RFID application but also provides low manufacturing cost, easy feeding, light weight, and easy integration into an environment with microwave components.After the introduction, this article is divided into 6 sections as mentioned below.Section 2 presents the design of the dipole antenna with its equivalent circuit.In Section 3, the split-ring resonator (SRR) with its equivalent circuit is studied.Then, the antenna design methodology using metamaterials is analyzed and studied with a parametric study to shed light on the effects of different parameters on the antenna performance.In Section 4, an analysis of the proposed antenna is performed in terms of return loss, current distribution, gain, and pattern.Finally, a comparison is made between the proposed antenna and the state of the art.

Dipole Antenna Configuration
Following previous studies in the literature [32][33][34], two symmetrical arms with dimensions W l × W d are printed on the top and bottom of the substrate to obtain a dipole antenna.This antenna is constructed on a 0.49 mm thick Arlon CuClad 250LX substrate with a relative permittivity of 2.42 and a loss tangent of 0.0018 and fed directly via a microstrip line to achieve a matching impedance of 50 Ω. Figure 1 shows the upper and lower view of the dipole antenna design.The original dipole antenna with overall dimensions of 131 6 × 34 × 0 49 mm 3 (equivalent to 0 39 λ 0 × 0 11 λ 0 × 0 0014 λ 0 ) is designed to be centered at 1 GHz, and the harmonic frequency, defined as f 1 , is 2 GHz.All design parameters are listed in Table 1.

2
International Journal of RF and Microwave Computer-Aided Engineering The dipole antenna can be modelled by its equivalent circuit diagram, as shown in Figure 2(a) [35].The circuit consists of inductive and capacitive load elements, whereby the two arms of the antenna are replaced by a series combination of capacitance and inductance and a parallel combination of resistance, capacitance, and inductance.
Define W 01 as the first resonant frequency and W 02 as the second resonant frequency at which the antenna's reactance vanishes.R 0 is the resistance at W 01 , and R 1 is the resistance at W 02 .
C 0 represents the antenna capacitance at a frequency f that is well below the first resonance, as specified in the following equation [35,36].
where a is the radius of the rectangle and h is the half-length.L 0 is chosen to resonate with C 0 at W 02 and L 1 is chosen to resonate with C 1 at W 02 [35,36].
The estimated values of C 1 , R 1 , and L 1 are determined at the resonant frequency W 01 , where the antenna reactance vanishes and the resistance equals R 0 [35,36].As can be seen in Figure 2(b), if the antenna is located in a lossless medium characterized by the dielectric constant ε = ε 0 • ε r and the permeability μ = μ 0 , L 0 and L 1 remain unchanged and where ε 0 is the dielectric constant in free space and ε r is the relative dielectric constant of the medium, while 2 shows the comparative study between the theoretical analysis and the simulated analysis for the dipole antenna.
The antenna layout was simulated with Computer Simulation Technology (CST) Microwave Studio and modelled and optimized with Advanced Design System Environment (ADS).With the optimized parameters shown in Figure 3, a good agreement of the S 11 results between the simulated antenna layout and the equivalent circuit diagram of the antenna modelled at 1 GHz can be achieved.

Split-Ring Resonator Configuration
This section presents a study of the split-ring resonator (SRR) with its equivalent circuit diagram.This resonator consists of a metal loop with a square shape and a gap on one side (Figure 4) [37].As shown in Figure 4(c), the splitring resonator is a type of RLC series resonant circuit.It consists of capacitive, inductive, and resistive load components, which are symbolized by L, C, and R, respectively.The equivalent circuit diagram of the split-ring resonator structure can be represented by two LC series resonant circuits Figure 2: Dipole antenna equivalent circuit [35] in (a) a free space and (b) a lossy medium.International Journal of RF and Microwave Computer-Aided Engineering connected in parallel.By adjusting the ring length and the gap between the rings, the split-ring resonator configuration allows precise control of the resonant frequency at which the wave couples into the ring and forms a standing wave, resulting in a high electric field inside the gap.This precise control of the resonant frequency is particularly useful to achieve narrow banding given the small electrical size of the split-ring resonator relative to the wavelength.Therefore, the resonant frequency of split-ring resonator essentially depends on the inductance L, which is determined in particular by the shape and size of the ring, the capacitance C, and the resistance of the ring R.Not only the resonant frequency but also the Q-factor of the resonant circuit can vary.The Q-factor is a measure of how sharply the split-ring resonator can distinguish between frequencies.A higher Q-factor indicates lower dissipative losses and better frequency selectivity.The Q-factor shows its dependence on the inductance L, capacitance C, and resistance R.This resistance represents the dissipative losses.It is a way of accounting for the energy that is dissipated as heat in the resonator and can directly influence on the (Q -factor) of the resonator.The Q-factor is higher when the resistance in the split-ring resonator equivalent circuit is low, which means that the resonator stores and releases energy more efficiently at its resonant frequency.Contrary, a higher resistance resulting in a lower Q-factor and higher losses leads to an effect on the performance of the splitring resonator in applications such as antennas.
Figure 4(b) shows the design of the single split-ring resonator (SRR) unit cell.The split-ring resonator is placed on an Arlon CuClad 250LX substrate [38] with a dielectric constant of ε r = 2 42 and a thickness of 0.49 mm.The dimensions of the split-ring resonator are L = 11 95 mm, gap = 3 3 mm, and W = 0 55 mm.In order to derive the reflection and transmission coefficients of the split-ring res-onator, two wave ports are made in the left and right areas of the box as can be seen in Figure 4(a).The curve of the reflection coefficient for the split-ring resonator cell is shown in Figure 5(a).The metamaterial has a transmission coefficient (S 12 ) of -45 dB and -48 dB when operating at a frequency of 2.5 GHz and 5.8 GHz, respectively.Figure 5(b) shows the real part of the effective permeability curve for a split-ring resonator.Based on equation (9) [31], it is obvious that the permeability in the frequency range of 2.41-2.8GHz has negative values exactly at the resonance point at 2.5 GHz.Similarly, this resonator has a second negative μ eff value around the resonant frequency 5.3 to 7 GHz.The presence of negative values for permeability highlights the particular behavior of the metamaterial and categorizes it as a lefthanded medium (LHM).To better understand how the split-ring resonator works, Figure 6 shows the distributions of surface currents within the split-ring resonator structure.This plot is shown specifically for the frequency corresponding to the operation of the split-ring resonator.It can be seen that the double resonant frequency is due to the inductive and capacitive effect that occurs in the metallic conductive paths and gab, respectively.
Before proceeding to the next section, let us discuss the reason for choosing the split-ring resonator in our proposed antenna design.The split-ring resonator offers advantages such as the following: (iii) Split-ring resonator can influence the impedance matching of the dipole antenna, as good impedance matching has been achieved in its dual band.Thus, efficient power transfer between the dipole antenna and the split-ring resonator can maximize the power radiated by the proposed metamaterial antenna Finally, we can assert that the decision to utilize splitring resonator over other resonators is based on its tailored suitability for achieving multiband antenna with high gain that aligns with our specific goals.

Antenna Design Methodology Using Metamaterials
In this section, the performance characteristics of a dipole antenna with an integrated split-ring resonator array are investigated in different orientations: 0 °, 90 °, 180 °, and 270 °(see Figure 7).The split-ring resonator array is positioned around the radiating element on the top and bottom of the Arlon CuClad 250LX substrate (see Figure 8) to investigate the effects of its orientation on the radiation characteristics of the dipole antenna, such as impedance matching and   Figure 9 shows the S-parameter simulations used to investigate the effect of the different split-ring resonator orientations on the reflection coefficient of the antennas.It can be observed that the S 11 curves in the UHF band show a high degree of consistency for all orientations, indicating similar antenna characteristics in this frequency range in all positions.The inclusion of a split-ring resonator array in the dipole antenna lowers the resonant frequency to 915 MHz    ).This could be due to a stronger electromagnetic interaction between the antenna and the split-ring resonator array.Conversely, in the SHF band, there is a clear divergence in the S 11 curve for a dipole antenna with a 0 °splitring resonator array.This divergence indicates a stronger influence on the operation of the antenna in the SHF frequency band when the split-ring resonator array is positioned at an angle of 0 °.The corresponding resonant frequencies for the dipole antenna with a 0 °split-ring resonator array are as follows: 0.88-0.97GHz, 2.37-2.46GHz, and 5.77-5.87GHz.The gap of the split-ring resonator changes the effective capacitance, which in turn changes the resonant frequencies.Consequently, the orientation of the gap in a (SRR) has a significant influence on the reflection coefficient of the antenna features.
Figure 10 shows the curve of the achieved gain for the dipole antenna with different split-ring resonator orientations at 0 °, 90 °, 180 °, and 270 °.Within the frequency band of 0.8-1 GHz, the realized gain remains almost the same for all antennas, with each having an estimated realized gain of 1.9 dB.At 2.4 GHz, a significant increase in realized gain to 6.5 dB is observed for dipole antennas with 0 °and 180 °split-ring resonator orientations, as compared to those with 90 °and 270 °split-ring resonator orientation, which means that split-ring resonator orientation at 0 °and 180 °has a greater impact on antenna performance at this specific frequency.In the entire SHF band, the achieved gain varies between 4 dB and 6.6 dB.The dipole antennas with 0 °and 180 °split-ring resonator show a slight improvement compared to the antennas with 90 °and 270 °SSR in the same frequency band.This observation indicates that 0 °and 180 °split-ring resonator orientations lead to better antenna performance in the UHF and SHF bands.Furthermore, the result shows that the symmetry of the split-ring resonator on the antenna has no influence on the overall performance.Therefore, certain split-ring resonator orientations could possibly contribute to improved antenna performance.
To simplify the analysis, we focus on specific antennas with split-ring resonator array orientations at 0 °, since the SRR orientation at 0 °is similar to that at 180 °.The innovative technique integrates the split-ring resonator array into the dipole antenna with an alternating arrangement, as shown in Figure 11.This arrangement method intentionally changes the interaction between the dipole antenna and the split-ring resonator array.Consequently, this modification can lead to changes in the electromagnetic coupling results and impedance matching characteristics.All design parameters are listed in Table 3.
Figure 12 shows the curve of the reflection coefficient for a dipole antenna with an alternating split-ring resonator array at 0 °.It can be observed that the antenna with a 0 °split-ring resonator array has peaks in certain frequency bands.These include 0.88-0.97GHz, 2.41-2.48GHz, and 5.77-5.91GHz.It is noticeable that these frequencies correspond well with the frequencies of the three-band RFID applications (860-960 MHz and 2.4 GHz/5.8GHz).As can be seen in Figure 12, the proposed antenna also shows excellent impedance matching at the resonant frequencies.
Figure 13 shows the curve of the realized gain of the proposed metamaterial antenna.Compared with Figure 10, the alternating arrangement of 0 °split-ring resonator arrays shows a higher realized gain, reaching 7 dB at the frequency of 2.47 GHz, which is consistent with the RFID frequency range, albeit with a slight upward shift.As can be seen in Figure 13, the antenna gain curve increases in the third range, showing a peak of 6 dB in the RFID frequency range from 5.725 GHz to 5.850 GHz and reaches a maximum of 7 dB at 5.91 GHz, with the maximum gain outside the frequency band of 5.8 GHz with a slight upward shift, representing a significant increase in performance.This is understandable as in a 0 °configuration, the split-ring 9 International Journal of RF and Microwave Computer-Aided Engineering resonator array runs parallel to the antenna elements, which can influence the direction of wave propagation and amplify the signal strength in a particular direction.To summarize, the alignment of the split-ring resonator array at 0 °with an alternating array integrated into the dipole antenna can significantly affect the performance of the antenna.Similar to the split-ring resonator equivalent circuit, the metamaterial antenna can also be simplified to a simple parallel LC tank circuit [39].However, to design an antenna based on SRRs, equivalent circuit models are required.SRRs can be excited both magnetically and electrically [40].However, it has been confirmed that magnetic coupling is the dominant mechanism in SRRs.The proposed equivalent circuit model for the loaded split-ring resonator antenna is shown in Figure 14.L 0 is the inductance of the dipole antenna, while the split-ring resonator is modelled as resonant tank circuits (with inductance L 2 and capacitance C 2 ) that are magnetically connected to the dipole antenna via a mutual      12 International Journal of RF and Microwave Computer-Aided Engineering   International Journal of RF and Microwave Computer-Aided Engineering inductance M. The values of inductance L 2 and capacitance C 2 can be obtained using the following equations [35,36].
where μ eff is the relative permeability and h is the halflength.L unit and L fp represent the additional inductance per unit length which can be calculated using the following equations [35,36]:

12
where ε r is the relative permittivity, μ r is the relative permeability, and μ 0 is the permeability in free space.F is an unknown factor that can be expressed as follows [35,36]: where the wave number K eff can be approximated by K eff = w/c ε eff μ eff , ε eff is the effective relative permittivity, w is the angular frequency, and K 0 is the free space wave number.Considering (3)-( 5), (10), and (11), the estimated values of circuit elements can be obtained and are indicated in Table 4.

Parametric Study and Optimization of the Proposed Antenna
Investigation through a parametric study is crucial to understand the impact of each parameter on antenna characteristics, paving the way for antenna effectiveness optimization.In this analysis, only a single parameter is adjusted while the others remain stable.By integrating a split-ring resonator array with a dipole antenna, an interesting physical phenomenon occurs, namely, W p , the spacing between the SRRs.This value plays a decisive role in determining the frequency at 2.47 GHz.This can be seen in Figure 15(a).A lower W p value leads to a higher capacitive effect, making the antenna more efficient at lower frequencies, while a higher W p value increases the resonant frequency, making the antenna suitable for higher frequencies.Furthermore, the influence of W p is not limited to frequency.It can also influence other important communicative properties such as the gain of the antenna.Changing the physical structure of the split-ring resonator array can change the radiation pattern and possibly transform the typical dipole antenna into a more directional structure, which improves the gain of the antenna up to 7.6 dB, as a smaller spacing between the rings generally leads to a higher gain (see Figure 15(b)).The realized gain can reach 8.3 dB with a further decrease in this parameter.
In addition, L g , which is the mutual capacitance between the ground plane and the split-ring resonator, can significantly influence the characteristics of the antenna.The value of L g can control the resonant frequency of the proposed metamaterial antenna at 5.8 GHz, as shown in Figure 16(a).When the value of L g is increased, the mutual capacitance decreases, which increases the resonant frequency due to the lower storage of electric field energy and leads to a higher resonant frequency.Conversely, if L g is reduced, the electrical length of the antenna increases, and the resonant frequency decreases, as the electric field increases due to the greater charge storage between the ground plane and the split-ring resonator array.Figure 16(a) therefore shows a direct relationship between L g and the resonant frequency of the proposed antenna.L g changes can also indirectly affect the radiation pattern and gain of the antenna by changing the current distribution.As can be seen in Figure 16(b), by adjusting the parameter L g , we can manip-ulate the realized gain of the antenna for specific applications, which underlines its central role in improving the performance of the antenna as needed.

Results and Discussion
6.1.Simulated Surface Current Analysis.The distribution of the surface current in a dipole antenna with an alternating arrangement of split-ring resonator arrays at 0 °orientation over different frequencies is shown in Figure 17.From Figure 17(a), it can be seen that the current mainly flows in the arms of the dipole antenna at 0.915 GHz, indicating that these parts mainly act as radiating elements.This frequency is close to the resonant frequency of the antenna without metamaterials.At 2.4 GHz (Figure 17(b)), the current peaks at the entire edge of the split-ring resonator array, suggesting that this frequency coincides with the resonant frequency of the split-ring resonator.At 5.8 GHz (Figure 17(c)), the current is mainly distributed between the split-ring resonator and the ground plane, indicating that this coupling leads to a response at this frequency.In addition, the current mainly circulates around the alternating split-ring resonator array, suggesting that their arrangement is affecting the behavior of the antenna.

Radiation Pattern and Efficiency.
The radiation patterns of the measurement and the simulation are shown both in the E plane and in the H plane at the individual resonance modes 0.915, 2.45, and 5.8 GHz (see Figure 18).A high degree of agreement is observed between the simulated and measured results.Furthermore, due to the symmetrical dipole structure, the antenna shows an omnidirectional radiation pattern in both planes above 0.915 GHz, as shown in Figure 18(a).At the frequency of 2.45 GHz, the result shows that the proposed antenna in combination with metamaterials has a directional radiation pattern in the E plane and H plane.As can be seen in Figure 18(b), the interaction of     .In contrast, a wider bandwidth (see the second SRR resonant frequency in Figure 5(a)) allows for more flexible operation over a range of frequencies.In summary, the resonator allows the antenna to operate over a wider frequency range with greater flexibility, which in turn affects the radiation pattern at 5.8 GHz.
The simulated and measured efficiencies of the metamaterial antenna are shown in Figure 19.The antenna shows peak overall efficiencies of 97%, 98%, and 95%, respectively, in the three operating bands.The proposed antenna offers stable efficiencies throughout.However, the efficiency decreases in the nonresonant band.Figure 19 shows a small discrepancy between the measured efficiency and the simulated efficiency curve.This can be attributed to several factors, such as the minimum spacing (W p = 0 5 mm and L g = 0 25 mm), which may have caused problems during fabrication or measurement, as the values of L g and W p play a crucial role in controlling the performance of the proposed antenna, as shown in Figures 15(b) and 16(b), and consequently may have a negative impact on the measured efficiency, or the placement of the antenna during the measurement setup.

Fabrication and Measurement.
To validate the numerical analysis, a prototype is fabricated (see Figure 20) and tested (see Figure 21) according to the final optimization to achieve the perfect antenna design.Figure 22 shows the simulated and measured S 11 of the proposed metamaterial antenna.Following the results, there is a great agreement between the simulated and tested results for S 11 , although there was a small shift in the tested results.This phenomenon could be due to several aspects, including the manufacturing discrepancy and the influence of the SMA connector.

State-of-the-Art Comparison
Table 5 contains a detailed comparison of the proposed antenna with other recent multiband antennas for similar applications.When evaluating the performance, it is noticeable that the gain of the microstrip antennas in the UHF band is at most 6 dB [11][12][13][14][15][16].Unfortunately, this is not an excellent result, as it can lead to losses in network coverage, especially for RFID, which limits their practical application.The antenna presented in this paper has a higher gain in certain frequency bands, especially in the UHF band, reaching up to 7 dB, which emphasizes the superiority of our design in this aspect.Moreover, the antennas in references [10,14,26] operate on two bands and have miniaturized size but are inadequate compared to our proposed design.This comparison shows that our antenna can cover more bands than the other designs.Importantly, the proposed antenna utilizes a simple geometry with a single probe feed, eliminating the need for a complex structure and multilayer substrate as called for in references [11,14].This design promotes low weight, low profile, and low fabrication cost due to the planar structure, which is a clear advantage of the proposed antenna.Comparing our design with the existing literature, it is clear that our proposed antenna outperforms the existing designs and establishes itself as a strong contender for RFID applications that require a high gain multiband antenna.

Conclusion
In this study, a high gain multiband antenna was analyzed and investigated by a novel approach of integrating a symmetrical split-ring resonator array with alternating array at 0 °orientation into a dipole antenna.The results of the work have shown that the proposed antenna design provides a clear discrimination between all operating bands in terms of good impedance matching and excellent efficiency.In addition, an in-depth parametric analysis was performed to understand the physics behind the antenna's performance enhancement without the need for augmentation or additional circuitry.The metamaterial antenna has several advantages, such as lighter weight and easy fabrication due to its simple design, and it can cover the triple band of RFID applications.

Figure 1 :
Figure 1: Design of dipole antenna: (a) top view, (b) bottom view, (c) side view, and (d) radius of the rectangle.

Figure 3 :
Figure 3: Simulated S 11 of the equivalent circuit and layout of the dipole antenna.

Figure 9 :
Figure 9: Simulated S 11 of the dipole antenna with different orientations of the split-ring resonator.

Figure 11 :
Figure 11: Geometry of the proposed dipole antenna with an alternating arrangement of split-ring resonator array at 0 °orientation and its equivalent circuit analysis.
antenna with 0° SRR array Dipole antenna with 90° SRR array Dipole antenna with 180° SRR array Dipole antenna with 270° SRR array

Figure 10 :
Figure 10: Simulated realized gain of the dipole antenna with different orientations of the split-ring resonator.

Figure 12 :
Figure 12: Simulated S 11 of the proposed dipole antenna with an alternating arrangement of split-ring resonator array at 0 °orientations.

Figure 13 :
Figure 13: Simulated realized gain of the proposed dipole antenna with an alternating arrangement of split-ring resonator array at 0 °orientations.

Figure 15 :Figure 16 :
Figure 15: The effect of parameter W p on (a) simulated S 11 and (b) simulated realized gain.

Figure 18 :
Figure 18: Simulated and measured radiation patterns of the proposed metamaterial dipole antenna at different frequencies, (a) 0.915 GHz, (b) 2.45 GHz, and (c) 5.8 GHz, in E and H planes.

Figure 19 :
Figure 19: Simulated and measured efficiencies of the dipole antenna with an alternating arrangement of split-ring resonator array at 0 °.

Figure 18 (
c) shows a clear deterioration of the radiation pattern at 5.8 GHz.This degradation can be attributed to the wider bandwidth exhibited by the split-ring resonator at this frequency.In other words, when the split-ring resonator has a narrow bandwidth (see the first SRR resonant frequency in Figure5(a)), the antenna shows a more specific response to the resonant frequency, which affects the directional radiation pattern in this range (this can be interpreted in VNA Proposed antenna Computer

Figure 21 :
Figure 21: Setup to measure S 11 parameter of the proposed antenna.

Figure 22 :
Figure 22: Simulated and measured S 11 of the proposed metamaterials antenna.

Table 2 :
Comparative study between the analyzed element values within and without the lossless medium and the simulated parameter values for the dipole antenna.

Table 4 :
Element values of equivalent circuit for metamaterial dipole antenna.

Table 5 :
Comparison of the proposed antenna with other recent multiband antennas for similar applications.