Research Article  Open Access
Caixia Feng, Yongqiang Kang, Lijuan Dong, Lihong Wang, "HighGain SIR DualBand Antenna Based on CSRREnhanced SIW for 2.4/5.2/5.8 GHz WLAN", International Journal of Antennas and Propagation, vol. 2020, Article ID 8725192, 10 pages, 2020. https://doi.org/10.1155/2020/8725192
HighGain SIR DualBand Antenna Based on CSRREnhanced SIW for 2.4/5.2/5.8 GHz WLAN
Abstract
This paper presents a dualband step impedance resonator (SIR) antenna based on metamaterialinspired periodic structure of coupled complementary splitring resonators substrateintegrated waveguide (CSRRSIW). The antenna supports wireless local area networks (WLAN) bands at 2.4/5.2/5.8 GHz. The CSRRs and two branches of the SIR element are etched on the top and bottom metal surfaces of the substrate. The SIR element produces a fundamental frequency f_{1} at 2.4 GHz and a second harmonic frequency f_{s2} at 5.7 GHz. Meanwhile, the CSRRs produces a resonant frequency at highfrequency band around 5.2 GHz, which can be combined with the second harmonic frequency f_{s2} at 5.7 GHz. The highfrequency bandwidth can then be broadened. The simulated and measured results show that the dual operation bands with bandwidths of 16% from 2.25 GHz to 2.64 GHz and 18.2% from 5 GHz to 6 GHz for S11 < −10 dB are achieved. Meanwhile, the proposed antenna has peak gains ranging from 6.5 dBi to 7 dBi and from 7 dBi to 7.7 dBi in the lower and upper bands, respectively. Compared with many previously reported dualband antenna designs, the proposed antenna achieves comparable bandwidth performance and larger gain per unit area with a relatively smaller size. Moreover, the simple structure renders the proposed antenna has the advantage of easyprocessable and costeffective implementation.
1. Introduction
Multiband band antennas are widely used in modern wireless systems, as well as radar [1]. Scholars have carried out a lot of prominent research works on the dualband antenna. In [2], a quasiYagi antenna with operating bands around 1.8, 2.4, and 3.5 GHz is proposed. The driver uniform impedance resonator (UIR) elements, arm 1 to arm 3, are excited at different frequencies as halfwave dipoles. In [3], a dualwideband dipole directional antenna is proposed. The antenna consists of a dipole with crooked arms and parasitic Γshaped branches and double reflecting floors. In [4], a dualband magnetoelectric antenna is proposed. A folded magnetic dipole antenna that is realized by a vertically assembled shorted patch is introduced to achieve wide bandwidth. In [5], a dualband linearly polarized tag antenna for indoor positioning systems is proposed. Ushaped invertedF antenna for the UHF band is designed to surround the dipole for the UWB band. In [6], a wideband threedimensional dualband magnetoelectric (ME) dipole antenna is presented for WLAN and WiMAX applications. A fullmetal rectangular director is loaded right above the ME dipole antenna and resonates at around 3.6 GHz due to the excitation of the long electric dipole. In [7], a dualband 3 × 2 antenna arrays with 10.6% from 2.3 to 2.56 GHz and 16.6% from 3 to 4.2 GHz bandwidths is proposed. The antenna is realized on a FR4 substrate and a PTFE substrate. A miniaturized dualband dipole array antenna consisting of two parallel 1 × 4 subarrays and threelayers of substrate for use in base stations is proposed in [8]. In [9], a 4 × 4 Ku/Ka dualband sharedaperture beam scanning antenna array is proposed. The concept of the structure reuse is described. To increase the aperture utilization efficiency, the Kuband antenna is employed as some sidewalls of the Kaband antenna. In [10], a metaresonatorinspired dualband antenna for 2.4/5.2 GHz WLAN applications is proposed. Dual band operation is achieved by utilizing stacking technique on a dogbone shaped dipole antenna. In [11], a conventional singleband printed antenna is loaded with vialess composite right/lefthanded (CRLH) unit cells to achieve multiband operation. The plane of broadband transition is perpendicular to the antenna, and the structure of the whole antenna is threedimensional. In [12], a mechanically reconfigurable dualband slot antenna with wide tuning ranges is proposed. Although the above dualband antennas realize good performance such as wideband or high gain, their structures are either threedimensional or multilayer, which require a rather demanding nonplanar fabrication process and are difficult to be integrated on the planar circuits. The novel fully planar SIW based on metamaterialinspired periodic structure of coupled complementary splitring resonators (CSRRSIW) is proposed in [13]. The CSRRSIW is an attractive candidate for a costeffective implementation of microwave antenna due to the fully planar structure and the associated ease of implementation [14].
In our prior work [15], a broadband bowtie antennabased CSRRSIW is proposed. It confirms that the CSRRSIW not only confines wave propagation within the waveguide but also radiates electromagnetic waves through the CSRRs. The CSRRs produce a resonant frequency, which can be combined with the two resonant frequencies produced by the bowtie patch and the feedline of the bowtie patch. The bandwidth can then be broadened. Moreover, the gain in the lowfrequency bandwidth is enhanced by decreasing the gap width of the CSRR.
In this article, the fully planar CSRRSIW is applied to the design of the dualband step impedance resonator (SIR) antenna for WLAN. First, the dualband working mechanism is studied, including the length of the SIR element and the width of the wider strip to the antenna performance. Finally, the effect of the tilt angle of the inclined feed lines on gain enhancement of the dualband CSRRSIW SIR antenna is discussed. Compared with the previously reported dualband antenna designs in [7–12], the proposed antenna achieves comparable bandwidth performance and larger gain per unit area with a relatively smaller size. In addition, the proposed antenna only consists of one layer of coppercoated substrate. It can be realized by ordinary etching techniques. Therefore, the proposed antenna structure has easyprocessable and costeffective implementation.
2. Design of SIR DualBand Antenna
2.1. Antenna Geometry
The proposed antenna is shown in Figure 1. The CSRRSIW is the same as that in [15]. The difference is that the main element is SIR, which can achieve a dual operation bands which consists of a fundamental frequency f_{1} and a second harmonic frequency f_{s2}. The CSRRs and two branches of the SIR element are etched on the top and bottom metal surfaces of the substrate. The substrate is Rogers 5880. The thickness of 0.504 mm and a dielectric constant of 2.2. Table 1 shows the dimensions of the proposed antenna.
(a)
(b)

2.2. DualBand Working Mechanism
To obtain a dualband working, we use the SIR as the main radiating element. For the SIR, the impedance of the narrow and wider strip is Z_{1} and Z_{2}, and the corresponding lengths is θ_{1} and θ_{2}, respectively. The resonance condition can be described as follows:where impedance ratio R_{z} is
To get a compact size, the electrical lengths θ_{1} and θ_{2} are given in [16] as
On this premise, the relationship between the second harmonic frequency f_{s2} and fundamental frequency f_{1} is given by
In this case, the appropriate resonant frequencies f_{s2} and f_{1} can be designed by adjusting the impedance ratio R_{z}. Compared with the UIR elements in [2], the SIR element has great degree of freedom in structure and design.
In this paper, we designed f_{1} and f_{s2} as 2.4 GHz and 5.7 GHz, respectively. Substituting f_{s2} and f_{1} into (4), we obtain R_{z} is about 0.6. Then, substituting R_{z} into (3), we obtain θ_{1} = θ_{2} = 37.8°. Then, we get the parameters of the SIR l_{2}, l_{3}, , and , as shown in Table 1.
In Figure 2, the current distribution over the antenna at 2.4 GHz, 5.2 GHz, and 5.7 GHz are shown. We observed from Figures 2(a) and 2(c) that the current is concentrated in the SIR element at f_{1} = 2.4 GHz and f_{s2} = 5.7 GHz. From Figure 2(b), the current is concentrated in the CSRRs at 5.2 GHz. That is to say, the SIR element produces a fundamental frequency f_{1} at 2.4 GHz and a second harmonic frequency f_{s2} at 5.7 GHz. Meanwhile, the CSRRs produces a resonant frequency at highfrequency band around 5.2 GHz.
(a)
(b)
(c)
Figure 3 shows the simulated S11 of the proposed SIR dualband antenna. In Figure 3, there are three resonant frequencies at f_{1} = 2.4 GHz, f_{2} = 5.2 GHz, and f_{s2} = 5.7 GHz. The circumference of the CSRR resonant ring is approximately λ/4 (λ is the wavelength at f_{2} = 5.2 GHz). By adjusting the structure parameters, f_{2} and f_{s2} can be combined with each other. The highfrequency bandwidth can then be broadened. In this case, a dualband dipole antenna based on CSRRSIW can be obtained.
2.3. Parametric Analysis
A parametric study of key parameters based on CST MWS is given to assist with the design procedure. The results show that the length of the SIR element l_{2} and l_{3}, the width of the wider strip , and the width of the ground plane are the key parameters that affects antenna performance. Figures 4–6 show the results.
In Figure 4, the effect of l_{2} on the S11 is shown. We observed that l_{2} mainly affects the resonance at fundamental frequency f_{1} and the second harmonic frequency f_{s2}. With the increase of l_{2}, the effective electrical length θ_{1} of the narrow strip and the whole electrical length of the SIR element increases. Therefore, the fundamental frequency f_{1} and the second harmonic frequency f_{s2} decrease with the increasing of l_{2}, as shown in Figure 4. In Figure 4, when l_{2} = 7 mm, there are three resonant frequencies: f_{1} = 2.6 GHz, f_{2} = 5.2 GHz, and f_{s2} = 5.9 GHz. The lower operation bandwidth is from 2.4 GHz to 2.75 GHz. When l_{2} = 8 mm, the resonance at f_{2} do not change, but f_{1} and f_{s2} decrease to 2.47 GHz and 5.8 GHz, respectively. The lower operation bandwidth is from 2.3 GHz to 2.65 GHz. When l_{2} = 9 mm, f_{1} and f_{s2} decreases to 2.4 GHz and 5.7 GHz, respectively. The widest lower operation bandwidth of 16.6% from 2.2 GHz to 2.6 GHz is obtained. The higher operation bandwidth is from 4.9 GHz to 6 GHz.
In Figure 5, the effect of on the S11 is shown. We observed that mainly affects the resonance at fundamental frequency f_{1} near about 2.4 GHz. With the increase of , the impedance ratio R_{z} of the SIR element decreases. And then the whole electrical length of the SIR decreases according to (1). Therefore, the fundamental frequency f_{1} increases with the increasing of , as shown in Figure 5. The effective electrical length θ_{1} of the narrow strip of the SIR element has no change, and then the second harmonic frequency f_{s2} almost has no change. In Figure 5, when = 2 mm, there are three resonant frequencies: f_{1} = 2.35 GHz, f_{2} = 5.2 GHz, and f_{s2} = 5.7 GHz. The lower operation bandwidth is from 2.2 GHz to 2.5 GHz. When = 3 mm, the resonance at f_{2} and f_{s2} do not change, but f_{1} increases to 2.4 GHz. The widest lower bandwidth from 2.2 GHz to 2.6 GHz is obtained. When = 4 mm, f_{1} increases to 2.45 GHz. And the lower operation bandwidth is from 2.3 GHz to 2.6 GHz.
The antenna is reduced in size by reducing the width of the ground plane . In Figure 6, the effect of on the S11 is shown. With the decrease of , the electrical size of the ground plane reduced, which gives rise to a narrow bandwidth. When = 32 mm, the dual operation bands with bandwidths of 16.6% from 2.2 GHz to 2.6 GHz and 19.2% from 4.95 GHz to 6 GHz for S11 < −10 dB are achieved. When = 29 mm, the bandwidth is 16% from 2.25 GHz to 2.64 GHz and 18.2% from 5 GHz to 6 GHz, respectively. When = 26 mm, the bandwidths narrowed further. In addition, a further reduction of would make the width of ground plane less than the length of the SIR dipole element, which leads to a decrease in unidirectional radiation and a decrease in antenna gain. From the above, we choose = 29 mm as the width of the proposed antenna.
3. The Effect of Parameter θ
The two branches of the SIR element are connected by the inclined feed lines on both sides of the CSRRSIW dualband antenna. In this section, the effect of the tilt angle θ on gain enhancement of the dualband CSRRSIW SIR antenna is discussed. Figure 7 shows the Efield distribution over the antenna for different θ, which clearly demonstrates that the Efield intensity increases significantly when θ = 20°, whether at 2.4 GHz or 5.5 GHz.
(a)
(b)
(c)
(d)
Figure 8 shows the effect of tilt angle θ on the peak antenna gain. With the increase of θ from 0° to 20°, the peak gain increases, which is equivalent to enlargement of the antenna aperture [17]. A tilt angle of θ = 20° is observed to provide an optimum gain performance. Over the lower frequency band of 2.25 GHz–2.64 GHz, the gain varies between 6.5 dBi–7 dBi, which corresponds to a gain enhancement of 1.2 dB–1.4 dB compared with the antenna with 0° tilt angle.
Over the higher frequency band of 5.03 GHz–6 GHz, the gain varies between 7.0 dBi–7.7 dBi, which corresponds to a gain enhancement of 1.7 dB–1.9 dB compared with the antenna with 0° tilt angle.
The radiation patterns of the antenna with feed line tilted by 20° and 0° at 2.4 GHz and 5.5 GHz are shown in Figure 9. The effective aperture increases with the parameter θ, which leads to lower sidelobe level and fronttoback ratio [18]. We observed that, with the feed line tilted by 20°, there is a distinct improvement in the sidelobe level; however, there is degradation in the backlobe level, especially in Eplane. From Figure 9(a), the backlobe level is about −20.3 dB and −12.2 dB, when θ = 0° and 20° at 2.4 GHz, respectively. From Figure 9(c), the backlobe level is about −10.7 dB and −8.2 dB, when θ = 0° and 20° at 5.5 GHz, respectively.
(a)
(b)
(c)
(d)
In addition, from Figures 7(a) and 7(b), the Efield is mainly concentrated in the SIR element at 2.4 GHz, but there is also a part of Efield distribution around the CSRRs and the intervals among the CSRRs. Moreover, the CSRRs are etched sidebyside on the top and bottom metal surfaces of the substrate, with the complementary gaps facing toward opposite directions. Therefore, there are certain phase difference in the Efield distribution around here. Therefore, even at 2.4 GHz, the maximum radiation patterns of Eplane have a deviation of less than 8, shown in Figure 9(a). From Figures 7(c) and 7(d), the CSRRs are similar to a slot array, and each CSRR has certain phase difference at 5.5 GHz. Therefore, the maximum radiation patterns of Eplane deviate a certain angle, as shown in Figure 9(c).
4. The Measured Results and Discussion
The realized antenna is shown in Figure 10. The network analyzer Agilent N5230C is used to measure the magnitude of S11. The simulated and measured S11 are shown in Figure 11. We observed that the lower operation band is 16% from 2.25 GHz to 2.64 GHz, and the higher operation band is 18.2% from 5 GHz to 6 GHz. The measured result agrees well with the simulated one.
(a)
(b)
Figure 12 shows the anechoic chamber and the testing system for antenna radiation pattern. Figure 13 shows the normalized radiation patterns. The measured result agrees well with the simulated one. Figure 14 shows the measured gain and radiation efficiency of the dualband CSRRSIW antenna. We observed that the gain within the operating frequency range is flat. Maximum gain of the antenna is found to be 7 dBi for the lower operation band and 7.7 dBi for higher operation band. Also, the radiation efficiency is higher than 82% for the dual operation bands.
(a)
(b)
(c)
(d)
The performances of the proposed dualband SIR antenna with the previously reported dualband or multifrequency antennas are compared, and the results are listed in Table 2. The proposed antenna achieves comparable bandwidth performance and larger gain per unit area with a relatively smaller size. Moreover, the simple structure renders that the proposed antenna has the advantage of easyprocessable and costeffective implementation.

5. Conclusion
A dualband SIR antenna based on metamaterialinspired CSRRSIW was proposed. The SIR element produces a fundamental frequency f_{1} at 2.4 GHz and a second harmonic frequency f_{s2} at 5.7 GHz. Meanwhile, the CSRRs produces a resonant frequency at highfrequency band around 5.2 GHz, which can be combined with the second harmonic frequency f_{s2}. The fabricated antenna provided a dual operation bands with bandwidths of 16% from 2.25 GHz to 2.64 GHz and 18.2% from 5 GHz to 6 GHz for S11 < −10 dB. The maximum gains of 7 dBi and 7.7 dBi for the lower and higher operation bands were obtained, respectively. The proposed antenna achieved comparable bandwidth performance and larger gain per unit area with a relatively smaller size. In addition, the proposed antenna has the advantage of costeffective implementation thanks to the simple structure.
Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
This work was supported by the Youth Science and Technology Research Foundation of Shanxi Province, China (201901D211432), Science and Technology Innovation Group of Shanxi Province, China (201805D131006), Science and Technology Innovation Program of Institutions of Higher Education of Shanxi Province, China (2020L0466), Key Research and Development Projects (Industry) of Datong, China (2019030), and General Science Projects of Shanxi Datong University (2019K1).
References
 N. Haider, D. Caratelli, and A. G. Yarovoy, “Recent developments in reconfigurable and multiband antenna technology,” International Journal of Antennas and Propagation, vol. 2013, Article ID 869170, 14 pages, 2013. View at: Publisher Site  Google Scholar
 Y. Ding, Y. C. Jiao, P. Fei, B. Li, and Q. T. Zhang, “Design of a multiband quasiyagitype antenna with CPWtoCPS transition,” IEEE Antennas and Wireless Propagation Letters, vol. 10, pp. 1120–1123, 2011. View at: Publisher Site  Google Scholar
 H. Zhang, Y.C. Jiao, and Z. Weng, “A novel dualwideband directional dipole antenna with double reflecting floors,” IEEE Antennas and Wireless Propagation Letters, vol. 16, pp. 1941–1944, 2017. View at: Publisher Site  Google Scholar
 K. He, S.X. Gong, and F. Gao, “A wideband dualband magnetoelectric dipole antenna with improved feeding structure,” IEEE Antennas and Wireless Propagation Letters, vol. 13, pp. 1729–1732, 2014. View at: Publisher Site  Google Scholar
 W. An, Z. Shen, and J. Wang, “Compact lowprofile dualband tag antenna for indoor positioning systems,” IEEE Antennas and Wireless Propagation Letters, vol. 16, pp. 400–403, 2017. View at: Publisher Site  Google Scholar
 J. Tao, Q. Feng, and T. Liu, “Dualwideband magnetoelectric dipole antenna with director loaded,” IEEE Antennas and Wireless Propagation Letters, vol. 17, no. 10, pp. 1885–1889, 2018. View at: Publisher Site  Google Scholar
 Z. Wang, G.x. Zhang, Y. Yin, and J. Wu, “Design of a dualband highgain antenna array for WLAN and WiMAX base station,” IEEE Antennas and Wireless Propagation Letters, vol. 13, pp. 1721–1724, 2014. View at: Publisher Site  Google Scholar
 M. Li, Q. Li, B. Wang, C. Zhou, and S. Cheung, “A miniaturized dualband base station array antenna using band notch dipole antenna elements and AMC reflectors,” IEEE Transactions on Antennas and Propagation, vol. 66, no. 6, pp. 3189–3194, 2018. View at: Publisher Site  Google Scholar
 Y. R. Ding and Y. J. Cheng, “Ku/ka dualband dualpolarized sharedaperture beam scanning antenna array with high isolation,” IEEE Transactions on Antennas and Propagation, vol. 67, no. 4, pp. 2337–2342, 2019. View at: Publisher Site  Google Scholar
 S. V. Pushpakaran, R. K. Raj, P. V. Vinesh, R. Dinesh, P. Mohanan, and K. Vasudevan, “A metaresonator inspired dual band Antenna for wireless applications,” IEEE Transactions on Antennas and Propagation, vol. 62, no. 4, pp. 2287–2291, 2014. View at: Publisher Site  Google Scholar
 K. Saurav, D. Sarkar, and K. V. Srivastava, “CRLH unitcell loaded multiband printed dipole antenna,” IEEE Antennas and Wireless Propagation Letters, vol. 13, pp. 852–855, 2014. View at: Publisher Site  Google Scholar
 I. T. Nassar, H. Tsang, D. Bardroff, C. P. Lusk, and T. M. Weller, “Mechanically reconfigurable, dualband slot dipole antennas,” IEEE Transactions on Antennas and Propagation, vol. 63, no. 7, pp. 3267–3271, 2015. View at: Publisher Site  Google Scholar
 M. Nitas, M.T. Passia, and T. V. Yioultsis, “Analysis and design of a CSRRbased fully planar substrateintegrated waveguide for millimeterwave circuits and antennas,” in Proceedings of the 2017 11th European Conference on Antennas and Propagation (EUCAP), pp. 19–24, Paris, France, March 2017. View at: Publisher Site  Google Scholar
 M.T. Passia, M. Nitas, and T. V. Yioultsis, “A fully planar antenna for millimeterwave and 5 G communications based on a new CSRRenhanced substrateintegrated waveguide,” in Proceedings of the 2017 International Workshop on Antenna Technology: Small Antennas, Innovative Structures, and Applications (iWAT), pp. 1–3, Athens, Greece, March 2017. View at: Publisher Site  Google Scholar
 C. Feng, T. Shi, and L. Wang, “Novel broadband bowtie antenna based on complementary splitring resonators enhanced substrateintegrated waveguide,” IEEE Access, vol. 7, pp. 12397–12404, 2019. View at: Publisher Site  Google Scholar
 M. Makimoto and S. Yamashita, Microwave Resonators and Filter for Wireless Communication, Springer, Berlin, Germany, 2001.
 A. Dadgarpour, B. Zarghooni, B. S. Virdee, and T. A. Denidni, “Millimeterwave highgain SIW endfire bowtie antenna,” IEEE Transactions on Antennas and Propagation, vol. 63, no. 5, pp. 2337–2342, 2015. View at: Publisher Site  Google Scholar
 G. Zhai, Y. Cheng, Q. Yin, L. Chiu, S. Zhu, and J. Gao, “Super high gain substrate integrated clampedmode printed logperiodic dipole array antenna,” IEEE Transactions on Antennas and Propagation, vol. 61, no. 6, pp. 3009–3016, 2013. View at: Publisher Site  Google Scholar
Copyright
Copyright © 2020 Caixia Feng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.