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A circularly polarized wide-band magneto-electric dipole antenna with simple structure for BTS applications
Int. J. Electron. Commun. (AEÜ) 105 (2019) 92–97
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
A circularly polarized wide-band magneto-electric dipole antenna with simple structure for BTS applications Pejman Mohammadi a,⇑, MirHamed Rezvani b, Tahereh Siahy a a b
Department of Electrical Engineering, Urmia Branch, Islamic Azad University, Urmia, Iran Young Researchers and Elite Club, Urmia Branch, Islamic Azad University, Urmia, Iran
a r t i c l e
i n f o
Article history: Received 15 February 2019 Accepted 12 April 2019
Keywords: Magneto-electric dipole antenna Circularly polarized BTS GSM CDMA LTE
a b s t r a c t A circularly polarized magneto-electric dipole antenna with wide frequency band for base transceiver station (BTS) is presented. The structure of the proposed antenna is composed of a cavity metallic reflector with defected side walls, two pairs of vertical and trapezoidal horizontal copper plates and a U-shaped feed line. Defected side walls of the metallic reflector are utilized to improve the gain, front to back ratio (FBR) and impedance matching. Electric dipole and quasi magnetic dipole are realized with horizontal plates and shorted vertical plates, respectively. The trapezoidal horizontal plates are employed to obtain circular polarization (CP) characteristic with 3-dB axial ratio bandwidth of 41% from 1.7 to 2.6 GHz. Experimental results show that the proposed antenna operates at frequency range of 1.4–2.8 GHz with S11 < 10 dB and 3-dB axial ratio of 1.8 dB and 2.1 dB for frequencies 1.9 GHz and 2.1 GHz, respectively. Furthermore, half-power beamwidth (HPBW) wider than 60.5° and the gain higher than 6.2 dBi are realized. Ó 2019 Elsevier GmbH. All rights reserved.
1. Introduction Nowadays, cellular communication systems play important role to provide mobile services for handset users considering their main performance and complementary equipment such as BTS antennas. Therefore, many studies and researches have been carried out to develop their performance [1–3] and equipment [4–9]. Global system for mobile (GSM), code division multiple access (CDMA) and long term evolution (LTE) services with allocated frequency bands of 1710–1880 MHz (GSM1800) and 1850–1990 MHz (GSM1900), 1920–2170 MHz (CDMA2000) and also 2300–2400 MHz (LTE2300) and 2500–2690 MHz (LTE2500), respectively are the most useful personal mobile communication services in the cellular networks [10,11]. Hence, many approaches are reported to design the appropriate BTS antennas that can be operated at mentioned frequency bands. But, it is worth noting that the BTS antennas with simple structure and low cost are the priority candidates for the practical applications in the cellular networks. Lots of antennas are reported for BTS applications according to mentioned details. For instance, a compact multiband antenna with tapered-slot that covers 1.5/2/2.5 GHz bands, is proposed in [4]. This antenna is fed by an L-shaped microstrip line and backed ⇑ Corresponding author. E-mail address: [email protected] (P. Mohammadi). https://doi.org/10.1016/j.aeue.2019.04.008 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.
by a long reflector that causes the total dimension to become large. In [5], a high gain dual-band antenna for LTE base station applications is presented. Despite the gain of the proposed antenna is high, it suffers from unstable radiation patterns and limited frequency range. Both proposed antennas in [6] and [7] are suitable for LTE services and have approximately same structures due to using C-shaped dipoles. Also, the dual-polarized (±45°) antennas using multilayer artificial magnetic conductor (AMC) [8] and k/2 printed dipoles [9] for base stations are presented. But it should be noticed that none of these antennas [4–9] provide CP characteristic. Obviously there are various methods to achieve CP characteristic such as using dual orthogonal arms and slanting edge defected ground structure (DGS) [12]. In [13], circular polarization is realized by using two crossed printed dipoles through a wideband feeding network with broadband 90° phase shift. Also, the CP feature can be accomplished by the parasitic elements [14]. Additionally, CP antennas with wide 3-dB beamwidth are reported. For example, a dual sense CP antenna with flexible frequency ratio and 3-dB beamwidth of higher than 86° is proposed in [15]. Also, a three-dimensional CP antenna with 3-dB beamwidth of greater than 170° is studied in [16]. Moreover, various magneto-electric dipole antennas are reported in [17–26]. For example, a novel low profile magnetoelectric dipole antenna with obtuse-triangular structure with frequency bandwidth 1.67–2.22 GHz is investigated in [17]. The
P. Mohammadi et al. / Int. J. Electron. Commun. (AEÜ) 105 (2019) 92–97
proposed antennas in [18] and [19] utilize a horizontal planar dipole and a vertically oriented folded shorted patch. The differences in these antennas are only in feed structures so that the presented antenna in [18] is excited by a coaxial feed without the need of an additional balun, but the designed antenna in [19] is fed by a coaxial feed that works as a balun. In [20] a broadband magnetoelectric dipole antenna with impedance bandwidth of 51.9% for LTE femtocell base stations is studied. Moreover, a magnetoelectric dipole antenna in which the magnetic dipole part is realized by a triangular-shaped has been implemented in [21]. However, these antennas [17–21] operate in linear polarization. It is worth noting that there are magneto-electric dipole antennas with circular polarization that are designed for base stations. For example, a wideband CP magneto-electric dipole antenna fed by a C-shaped structure with frequency range 1.6–3.72 GHz is investigated in [22]. Also, a dual-band circularly polarized magneto-electric antenna with frequency bands 2.15–3.4 GHz and 4–6.3 GHz is proposed in [23]. But, it should be kept in mind that the frequency range of higher than 2.8 GHz is almost dispensable for BTS applications like the antennas in [22] and [23]. Therefore, using any techniques for improving the frequency bandwidth cause the antenna structures toward to be complicated. Additionally, the presented antenna in [23] does not cover GSM1800 and GSM1900 services. Other magneto-electric antennas for dual-band applications [24,25] and ±45° dual-polarized characteristic [26] are proposed. This paper proposes a wide-band magneto-electric dipole antenna with CP characteristics for femtocell applications. The antenna operates at the frequency range of 1.4–2.8 GHz with S11 less than 10 dB. Gain and HPBW higher than 6.2 dBi and wider than 60.5°, have been achieved respectively. Therefore, it can be used for GSM1800, GSM1900, CDMA2000, LTE2300 and LTE2500 services.
reflector. To achieve the circular polarization, the horizontal plates are designed like a trapezoidal shape. It is worthwhile mentioning that, not only circular polarization is obtained by these plates, but also the gain, FBR and S-parameter can be enhanced using this approach. A wide frequency bandwidth is realized in the light of optimized dimensions U-shaped feed structure. A hole with radius of 3 mm is punched on the reflector to access the SMA connector for exciting. Fig. 2 shows the side view and top view of the antenna and U-shaped feed structure, respectively. As illustrated in this figure, horizontal branch of U-shaped feed has an angle of h = 60° with respect to the Y-axis coordinate. The detailed dimensions of the radiation elements and U-shaped feed structure are indicated in Fig. 3 and summarized in Table 1. In order to investigate of the circular polarization mechanism, the surface current distributions of the trapezoidal horizontal plates (electric dipole) at different time phases of 0°, 45°, 90° and 135° for frequencies of 1.9 GHz and 2.1 GHz are shown in Fig. 4 (a–h). It can be observed that when the phase is 0°, 45°, 90° and 135°, the surface currents on the electric dipoles move along the direction of –X-axis coordinate in both frequencies. In other words, surface currents rotate in counterclockwise direction. Therefore, it can be concluded that a right-handed circular polarization (RHCP) in Z-axis direction produces at frequencies of 1.9 GHz and 2.1 GHz. 3. Parametric study and experimental results The proposed magneto-electric dipole antenna is simulated and analyzed by the Ansoft HFSS v.15 software. As it mentioned in the
2. Design and configuration of the antenna The 3-D view of the proposed magneto-electric dipole antenna is shown in Fig. 1. It can be seen that the antenna consists of a reflector (Lr Lr) with defected side walls (L1 Hr and L2 Hr), U-shaped feed structure and two pairs of radiation elements. The metallic reflector with thickness of 0.4 mm is utilized to suppress the back lope radiation and also the defected side walls are employed to increase the gain, FBR and impedance matching. The radiation elements are located in the center area of the reflector. Moreover, each radiation element is containing of the vertical palate as magnetic dipole and trapezoidal horizontal plate as electric dipole. The vertical plates are electrically connected to the
Fig. 2. Side view and top view of the proposed antenna.
Fig. 1. 3-D view of the proposed magneto-electric antenna.
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Fig. 3. Geometry of the proposed antenna.
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P. Mohammadi et al. / Int. J. Electron. Commun. (AEÜ) 105 (2019) 92–97
previous section, the defected side walls of the metallic reflector have significant effects on the gain, FBR, AR and impedance matching. These effects are shown in Fig. 5. Considering Fig. 5(a), the S-parameter is reduced by almost 20 dB and 5 dB without the side walls and with closed side walls, respectively especially around frequency 2 GHz. According to Fig. 5(b), despite the value of axial ratio without side walls is better than that with defected side walls, but it can be observed that the axial ratio is shifted approximately by 200 MHz from 1.9 GHz to 1.7 GHz that can be covered GSM1800 services. Also, axial ratio with closed side walls is unsatisfactory around 2–2.25 GHz. Additionally, the defected side walls not only enhance the gain, but it significantly improves the FBR value considering Fig. 5(c) and (d). In order to achieve circular polarization performance, trapezoidal horizontal plates are chosen as electric dipole. The advantages of the trapezoidal plates compared to the rectangular plates are demonstrated in Fig. 6. Obviously, the S-parameter is better than with trapezoidal plates due to Fig. 6(a). Also, consider-
ing Fig. 6(b) it can be concluded that the CP characteristic with axial ratio less than 3 dB is realized using trapezoidal plates. Moreover, the effects of these plates are also evaluated for gain and FBR and the results are shown in Fig. 6(c) and (d), respectively. The value of gain with trapezoidal plates is more stable compered to rectangular plates. Also, the FBR has a satisfactory result using trapezoidal plates. A U-shaped feed structure is adopted between the radiation elements. This simple U-shaped feed structure can well excite the radiation elements by optimizing its width (W1). In the other word, the most appropriate impedance matching is obtained by chosen a suitable width. Hence, different amounts of W1 are analyzed and their effects on S11 and input impedance are illustrated in Fig. 7 (a) and (b), respectively. When W1 decreases from 4 mm to 2 mm, S11 at frequency 2 GHz reaches to 10 dB while the frequencies higher and lower than 2 GHz are almost stable. Also, considering Fig. 7(b) it can be interpreted that these varieties have a relation with input impedance that is relatively changes with
Table 1 Specified dimensions of the presented antenna. Parameters
Lr
L1
L2
L3
L4
L5
L6
L7
Value (mm) Parameters Value (mm)
150 L8 22.9
132 Hr 30
135 H1 42
25 H2 42
50 H3 20
39.3 W1 4
84 h 60
20.4 G 2
Fig. 4. Simulated current distribution at different time phases of 0°, 45°, 90° and 135° for frequencies of 1.9 GHz and 2.1 GHz.
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respect to S11. On the other hand, when W1 increases from 4 mm to 6 mm, the value of S-parameter is significantly increased and the input impedance is decreased and reached to almost 30 X. Simulated radiation patterns of the antenna at xoz-plane and yozplane at frequencies 1.9 GHz and 2.1 GHz are plotted in Fig. 8(a) and (b), respectively. According to these plots, the proposed antenna provides RHCP with a good performance and low cross polarization (LHCP) with values of less than 20 dB at 1.9 GHz and 10 dB at 2.1 GHz. The concept of right-handed circular polarization has already been mentioned in the previous section by the indicated surface current distributions in Fig. 4.
Fig. 5. Simulated results of the proposed antenna with defected side walls, closed side walls and without side walls. (a) S11, (b) axial ratio, (c) gain and (d) FBR.
Fig. 8. Simulated radiation patterns of the proposed antenna at xoz-plane and yoz-plane at (a) 1.9 GHz and (b) 2.1 GHz.
Fig. 6. Simulated results of the proposed antenna with trapezoidal-shaped and rectangular-shaped dipoles. (a) S11, (b) axial ratio, (c) gain and (d) FBR.
Fig. 7. Simulated results of (a) S11 and (b) input impedance for various amounts of W1.
Fig. 9. Implementation of the proposed magneto-electric dipole antenna.
Fig. 10. Measured and simulated results of S11.
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The prototype of the proposed magneto-electric dipole antenna is implemented with copper material and the measurement process of far-filed parameters is conducted in an anechoic chamber. Also, S11 is measured by the Keysight N5242A PNA-X network analyzer. The implementation of the magneto-electric dipole antenna is shown in Fig. 9. The measured and simulated S-parameter of the proposed magneto-electric dipole antenna is illustrated in Fig. 10. As observed in this figure, the measured frequency bandwidth is from 1.4 GHz to 2.8 GHz with S11 < 10 dB while the simulated one is from 1.5 GHz to 2.7 GHz. It is worth noting that the obtained frequency range can be used for GSM1800 (1710–1880 MHz), GSM1900 (1850–1990 MHz), CDMA2000 (1920–2170 MHz), LTE2300 (2300–2400 MHz) and LTE2500 (2500–2690 MHz) services. The measured and simulated axial ratio is also shown in Fig. 11. It can be seen that, the axial ratio bandwidth (ARBW) is less than input impedance bandwidth but, it completely covers the mentioned services. The simulated 3-dB AR bandwidth is 41% from
Table 2 Overall specifications of the proposed antenna. Simulated FC [GHz] S11 [dB] Gain [dBi] FBR [dBi] HPBW [deg] AR [dB]
Fig. 12. Measured and simulated results of gain and FBR.
1.9 29.9 9.1 21.1 67 1.7
2.1 37.1 9.5 21.4 75 2.4
1.9 12 6.2 15.8 60.5 1.8
2.1 14 6.3 18.5 63.5 2.1
Table 3 Comparison between the proposed antenna and previous works. Ref.
BW [GHz]
Gain [dBi]
CP
Size [mm3]
[17] [18] [19] [20] [21] [22] [23]
1.67–2.22 1.88–3.3 1.86–2.96 1.62–2.81 1.83–2.73 1.35–4.2 2.15–3.4 4–6.3 1.4–2.8
9.2 ± 1.1 8.6 ± 0.8 8.1 ± 0.8 >6.6 8.4 ± 0.2 >5.4 >8
U U
152 152 15 112 112 19 130 130 21 120 120 30 150 150 21 150 130 30 100 100 30.3
>6.2
U
150 150 42
This work
Fig. 11. Measured and simulated results of axial ratio.
Measured
1.7 to 2.6 GHz. Also, the measured ARBW has good agreement with the simulated one. Fig. 12 is depicted measured and simulated gain and FBR. As shown in this figure, the measured results are lower than simulated one due to the fabrication errors and environment effectives; however, these results are still satisfactory for practical standards. The measured gain is 6.2 dBi and 6.3 dBi at frequencies 1.9 GHz and 2.1 GHz, respectively. In addition, the measured FBR is 15.8 dB and 18.5 dB at frequencies 1.9 GHz and 2.1 GHz, respectively. Fig. 13(a) and (b) are indicated measured and simulated radiation patterns at xoz-plane. Considering these plots, low differences between the simulated and measured RHCP are observed. The tolerance between the simulated and measured LHCP is impressive, but it is satisfactory result. Also, HPBWs of 60.5° for frequency 1.9 GHz and 63.5° for frequency 2.1 GHz are realized that are appropriate for BTS applications according to required standards of base stations. All measured and simulated results of the proposed magnetoelectric dipole antenna are summarized in Table 2. Moreover, a comparison between the previous magneto-electric dipole antennas [17–23] with the proposed antenna in this article that have approximately same structures and specifications is conducted and the results are indicated in Table 3. It can be concluded that the proposed antenna in this article has wider frequency bandwidth and benefits from CP characteristic and it has simpler structure as well. Despite CP characteristic and wide frequency bandwidth in [22], it has lower gain at frequency range 1.5– 2 GHz compared to the proposed antenna in this article. Also, the proposed CP magneto-electric dipole antenna in [23] has satisfactory performance but it does not cover GSM1800, GSM1900 and CDMA2000 services.
4. Conclusion
Fig. 13. Measured and simulated results of radiation patterns at (a) 1.9 GHz and (b) 2.1 GHz.
A wide-band CP magneto-electric dipole antenna is studied in this article. The proposed antenna consists of a metallic reflector with defected side walls to enhance the gain, FBR and impedance matching as well. The vertical and trapezoidal horizontal plates are utilized to realize magnetic and electric dipoles, respectively. The U-shaped feed structure is employed to excite the magnetoelectric dipole element and also using optimization of its dimensions the wide frequency bandwidth is realized. The mechanism
P. Mohammadi et al. / Int. J. Electron. Commun. (AEÜ) 105 (2019) 92–97
of CP characteristic is analyzed and shown that the trapezoidalshaped electric dipole has the main role to obtain axial ratio of less than 3 dB. According to measured results, the proposed antenna operates at frequency range 1.4–2.8 GHz that can be covered GSM1800, GSM1900, CDMA2000, LTE2300 and LTE2500 services. Considering the operating frequency range, satisfactory HPBW and gain and also a simple structure, the proposed antenna is the proper candidate for femtocell applications due to the GSM, CDMA and LTE services. Conflict of interest The authors declared that there is no conflict of interest.
[9] [10] [11]
[12]
[13]
[14]
Acknowledgment
[15]
The authors would like to acknowledge the Microwave and Antenna Research Center, Urmia Branch, Islamic Azad University, Urmia, Iran for measurement of the proposed antenna.
[16]
[17]
References [1] Jovanovic Predrag, Bjelica Milan. Estimation of GSM base station output power cumulative density function. AEU - Int J Electron Commun 2014;68:717–9. [2] Mitic Dragan, Lebl Aleksandar, Markov Zarko. Influence of traffic model on the calculation of BTS output power in GSM network. AEU - Int J Electron Commun 2015;69:836–40. [3] Choi Woo-Yong. A method for determining the number of Base stations connected to a BSC in CDMA cellular communication systems. AEU - Int J Electron Commun 2002;6:367–72. [4] Itoh Kazuya, Konno Keisuke, Chen Qiang. Shingo Inoue. Design of compact multiband antenna for triple-band cellular base stations. IEEE Antenn Wirel Propag Lett 2015;14:64–7. [5] Najafnezhad Elnaz, Nourinia Javad, Ghobadi Changiz, Majidzadeh Maryam, Mirzamohammadi Farnaz. A high gain dual-band printed antenna for LTE base stations with a corner reflector. AEU - Int J Electron Commun 2018;87:173–9. [6] Rezvani MirHamed, Mohammadi Pejman. Microstrip antenna with aperture reflector and C-shaped dipoles for LTE and wireless communications. AEU - Int J Electron Commun 2018;94:12–8. [7] Govindanarayanan Idayachandran, Rangaswamy Nakkeeran. Asymmetric folded dipole antenna with high front-to-back ratio for LTE base stations. IEEE Antenn Wirel Propag Lett 2015;15:869–72. [8] Rajagopal Senthilkumar, Chennakesavan Gokulnath, Subburaj Deepak Ram Prasath, Srinivasan Raju, Varadhan Abhaikumar. A dual polarized antenna on a novel broadband multilayer artificial magnetic conductor backed surface for
[18] [19] [20]
[21] [22]
[23]
[24]
[25]
[26]
97
LTE/CDMA/GSM base station applications. AEU - Int J Electron Commun 2017;80:73–9. Rezvani M, Mohammadi P. A dual-polarized reflector antenna with k/2 printed dipoles for femtocell applications. J Instrum 2019;14:P02004. Dai Xi-Wang, Zhou Tao. Dual-band reflectarray with crossed-dipole elements for GSM and LTE applications. AEU - Int J Electron Commun 2016;70:605–10. Dai Xi-Wang, Zhou Xiao-Yu, Luo Guo-Qing. Wideband directional antenna system with different polarizations for wireless communication system. AEU Int J Electron Commun 2017;75:119–23. Tejpal Vivekanand Tiwari, Bhatnagar Deepak, Yadav Dinesh, Rawat Sanyog. A dual-band CP dual-orthogonal arms monopole antenna with slanting edge DGS for C-band wireless applications. AEU - Int J Electron Commun 2018;84:251–7. Li Chao, Zhang Fushun, Zhang Fan, Yang Kaiwen. A wideband circularly polarized antenna with wide beamwidth for GNSS applications. Prog Electromag Res C 2018;84:189–200. Choi Eun-cheol, Lee Jae W, Lee Taek-Kyung, Lee Woo-Kyung. Circularly polarized s-band satellite antenna with parasitic elements and its arrays. IEEE Antenn Wirel Propag Lett 2014;13:1689–92. Li Jianxing, Shi Junwei, Li Lumei, Khan Tayyab Ali, Chen Juan, Li Yingsong, Zhang Anxue. Dual-band annular slot antenna loaded by reactive components for dual-sense circular polarization with flexible frequency ratio. IEEE Access 2018;6:64063–70. Li Yingsong, Mittra Raj. A three-dimensional circularly polarized antenna with a low profile and a wide 3-dB beamwidth. J Electromag Waves Appl 2016;30:89–97. Ding Chen, Luk Kwai-Man. Low-profile magneto-electric dipole antenna. IEEE Antenn Wirel Propag Lett 2016;15:1642–4. Ge Lei, Luk Kwai Man. A low-profile magneto-electric dipole antenna. IEEE Trans Antenn Propag 2012;60:1684–9. Ge Lei, Luk Kwai Man. A magneto-electric dipole antenna with low-profile and simple structure. IEEE Antenn Wirel Propag Lett 2013;12:140–2. Govindanarayanan Idayachandran, Rangaswamy Nakkeeran, Anbazhagan Rajesh. Design and analysis of broadband magneto-electric dipole antenna for LTE femtocell base stations. J Comput Electron 2016;15:200–9. Luk Kwai-Man, Biqun Wu. The magnetoelectric dipole—a wideband antenna for base stations in mobile communications. Proc IEEE 2012;100:2297–307. Feng Chao-Qiang, Zhang Fu-Shun, Zhang Han-Jing, Jun-Xiu Su. A single-feed circularly polarized magnetoelectric dipole antenna for wideband wireless applications. Prog Electromag Res M 2018;65:1–8. Tao Jun, Feng Quanyuan. Dual-band magnetoelectric dipole antenna with dual-sense circularly polarized character. IEEE Trans Antenn Propag 2017;65:5677–85. Feng Botao, Lia Shufang, An Wenxing, Hong Weijun, Wang Shuai, Yin Sixing. A printed dual-wideband magneto-electric dipole antenna for WWAN/LTE applications. AEU - Int J Electron Commun 2014;68:926–32. An Wen Xing, Wong Hang, Lau Ka Leung, Li Shu Fang, Xue Quan. Design of broadband dual-band dipole for base station antenna. IEEE Trans Antenn Propag 2012;60:1592–5. Li Zuming, Sun Yufa, Yang Ming, Zhifeng Wu, Tang Peiquan. A broadband dualpolarized magneto-electric dipole antenna for 2G/3G/LTE/WiMAX applications. Prog n Electromag Res C 2017;73:127–36.
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
A circularly polarized wide-band magneto-electric dipole antenna with simple structure for BTS applications Pejman Mohammadi a,⇑, MirHamed Rezvani b, Tahereh Siahy a a b
Department of Electrical Engineering, Urmia Branch, Islamic Azad University, Urmia, Iran Young Researchers and Elite Club, Urmia Branch, Islamic Azad University, Urmia, Iran
a r t i c l e
i n f o
Article history: Received 15 February 2019 Accepted 12 April 2019
Keywords: Magneto-electric dipole antenna Circularly polarized BTS GSM CDMA LTE
a b s t r a c t A circularly polarized magneto-electric dipole antenna with wide frequency band for base transceiver station (BTS) is presented. The structure of the proposed antenna is composed of a cavity metallic reflector with defected side walls, two pairs of vertical and trapezoidal horizontal copper plates and a U-shaped feed line. Defected side walls of the metallic reflector are utilized to improve the gain, front to back ratio (FBR) and impedance matching. Electric dipole and quasi magnetic dipole are realized with horizontal plates and shorted vertical plates, respectively. The trapezoidal horizontal plates are employed to obtain circular polarization (CP) characteristic with 3-dB axial ratio bandwidth of 41% from 1.7 to 2.6 GHz. Experimental results show that the proposed antenna operates at frequency range of 1.4–2.8 GHz with S11 < 10 dB and 3-dB axial ratio of 1.8 dB and 2.1 dB for frequencies 1.9 GHz and 2.1 GHz, respectively. Furthermore, half-power beamwidth (HPBW) wider than 60.5° and the gain higher than 6.2 dBi are realized. Ó 2019 Elsevier GmbH. All rights reserved.
1. Introduction Nowadays, cellular communication systems play important role to provide mobile services for handset users considering their main performance and complementary equipment such as BTS antennas. Therefore, many studies and researches have been carried out to develop their performance [1–3] and equipment [4–9]. Global system for mobile (GSM), code division multiple access (CDMA) and long term evolution (LTE) services with allocated frequency bands of 1710–1880 MHz (GSM1800) and 1850–1990 MHz (GSM1900), 1920–2170 MHz (CDMA2000) and also 2300–2400 MHz (LTE2300) and 2500–2690 MHz (LTE2500), respectively are the most useful personal mobile communication services in the cellular networks [10,11]. Hence, many approaches are reported to design the appropriate BTS antennas that can be operated at mentioned frequency bands. But, it is worth noting that the BTS antennas with simple structure and low cost are the priority candidates for the practical applications in the cellular networks. Lots of antennas are reported for BTS applications according to mentioned details. For instance, a compact multiband antenna with tapered-slot that covers 1.5/2/2.5 GHz bands, is proposed in [4]. This antenna is fed by an L-shaped microstrip line and backed ⇑ Corresponding author. E-mail address: [email protected] (P. Mohammadi). https://doi.org/10.1016/j.aeue.2019.04.008 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.
by a long reflector that causes the total dimension to become large. In [5], a high gain dual-band antenna for LTE base station applications is presented. Despite the gain of the proposed antenna is high, it suffers from unstable radiation patterns and limited frequency range. Both proposed antennas in [6] and [7] are suitable for LTE services and have approximately same structures due to using C-shaped dipoles. Also, the dual-polarized (±45°) antennas using multilayer artificial magnetic conductor (AMC) [8] and k/2 printed dipoles [9] for base stations are presented. But it should be noticed that none of these antennas [4–9] provide CP characteristic. Obviously there are various methods to achieve CP characteristic such as using dual orthogonal arms and slanting edge defected ground structure (DGS) [12]. In [13], circular polarization is realized by using two crossed printed dipoles through a wideband feeding network with broadband 90° phase shift. Also, the CP feature can be accomplished by the parasitic elements [14]. Additionally, CP antennas with wide 3-dB beamwidth are reported. For example, a dual sense CP antenna with flexible frequency ratio and 3-dB beamwidth of higher than 86° is proposed in [15]. Also, a three-dimensional CP antenna with 3-dB beamwidth of greater than 170° is studied in [16]. Moreover, various magneto-electric dipole antennas are reported in [17–26]. For example, a novel low profile magnetoelectric dipole antenna with obtuse-triangular structure with frequency bandwidth 1.67–2.22 GHz is investigated in [17]. The
P. Mohammadi et al. / Int. J. Electron. Commun. (AEÜ) 105 (2019) 92–97
proposed antennas in [18] and [19] utilize a horizontal planar dipole and a vertically oriented folded shorted patch. The differences in these antennas are only in feed structures so that the presented antenna in [18] is excited by a coaxial feed without the need of an additional balun, but the designed antenna in [19] is fed by a coaxial feed that works as a balun. In [20] a broadband magnetoelectric dipole antenna with impedance bandwidth of 51.9% for LTE femtocell base stations is studied. Moreover, a magnetoelectric dipole antenna in which the magnetic dipole part is realized by a triangular-shaped has been implemented in [21]. However, these antennas [17–21] operate in linear polarization. It is worth noting that there are magneto-electric dipole antennas with circular polarization that are designed for base stations. For example, a wideband CP magneto-electric dipole antenna fed by a C-shaped structure with frequency range 1.6–3.72 GHz is investigated in [22]. Also, a dual-band circularly polarized magneto-electric antenna with frequency bands 2.15–3.4 GHz and 4–6.3 GHz is proposed in [23]. But, it should be kept in mind that the frequency range of higher than 2.8 GHz is almost dispensable for BTS applications like the antennas in [22] and [23]. Therefore, using any techniques for improving the frequency bandwidth cause the antenna structures toward to be complicated. Additionally, the presented antenna in [23] does not cover GSM1800 and GSM1900 services. Other magneto-electric antennas for dual-band applications [24,25] and ±45° dual-polarized characteristic [26] are proposed. This paper proposes a wide-band magneto-electric dipole antenna with CP characteristics for femtocell applications. The antenna operates at the frequency range of 1.4–2.8 GHz with S11 less than 10 dB. Gain and HPBW higher than 6.2 dBi and wider than 60.5°, have been achieved respectively. Therefore, it can be used for GSM1800, GSM1900, CDMA2000, LTE2300 and LTE2500 services.
reflector. To achieve the circular polarization, the horizontal plates are designed like a trapezoidal shape. It is worthwhile mentioning that, not only circular polarization is obtained by these plates, but also the gain, FBR and S-parameter can be enhanced using this approach. A wide frequency bandwidth is realized in the light of optimized dimensions U-shaped feed structure. A hole with radius of 3 mm is punched on the reflector to access the SMA connector for exciting. Fig. 2 shows the side view and top view of the antenna and U-shaped feed structure, respectively. As illustrated in this figure, horizontal branch of U-shaped feed has an angle of h = 60° with respect to the Y-axis coordinate. The detailed dimensions of the radiation elements and U-shaped feed structure are indicated in Fig. 3 and summarized in Table 1. In order to investigate of the circular polarization mechanism, the surface current distributions of the trapezoidal horizontal plates (electric dipole) at different time phases of 0°, 45°, 90° and 135° for frequencies of 1.9 GHz and 2.1 GHz are shown in Fig. 4 (a–h). It can be observed that when the phase is 0°, 45°, 90° and 135°, the surface currents on the electric dipoles move along the direction of –X-axis coordinate in both frequencies. In other words, surface currents rotate in counterclockwise direction. Therefore, it can be concluded that a right-handed circular polarization (RHCP) in Z-axis direction produces at frequencies of 1.9 GHz and 2.1 GHz. 3. Parametric study and experimental results The proposed magneto-electric dipole antenna is simulated and analyzed by the Ansoft HFSS v.15 software. As it mentioned in the
2. Design and configuration of the antenna The 3-D view of the proposed magneto-electric dipole antenna is shown in Fig. 1. It can be seen that the antenna consists of a reflector (Lr Lr) with defected side walls (L1 Hr and L2 Hr), U-shaped feed structure and two pairs of radiation elements. The metallic reflector with thickness of 0.4 mm is utilized to suppress the back lope radiation and also the defected side walls are employed to increase the gain, FBR and impedance matching. The radiation elements are located in the center area of the reflector. Moreover, each radiation element is containing of the vertical palate as magnetic dipole and trapezoidal horizontal plate as electric dipole. The vertical plates are electrically connected to the
Fig. 2. Side view and top view of the proposed antenna.
Fig. 1. 3-D view of the proposed magneto-electric antenna.
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Fig. 3. Geometry of the proposed antenna.
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previous section, the defected side walls of the metallic reflector have significant effects on the gain, FBR, AR and impedance matching. These effects are shown in Fig. 5. Considering Fig. 5(a), the S-parameter is reduced by almost 20 dB and 5 dB without the side walls and with closed side walls, respectively especially around frequency 2 GHz. According to Fig. 5(b), despite the value of axial ratio without side walls is better than that with defected side walls, but it can be observed that the axial ratio is shifted approximately by 200 MHz from 1.9 GHz to 1.7 GHz that can be covered GSM1800 services. Also, axial ratio with closed side walls is unsatisfactory around 2–2.25 GHz. Additionally, the defected side walls not only enhance the gain, but it significantly improves the FBR value considering Fig. 5(c) and (d). In order to achieve circular polarization performance, trapezoidal horizontal plates are chosen as electric dipole. The advantages of the trapezoidal plates compared to the rectangular plates are demonstrated in Fig. 6. Obviously, the S-parameter is better than with trapezoidal plates due to Fig. 6(a). Also, consider-
ing Fig. 6(b) it can be concluded that the CP characteristic with axial ratio less than 3 dB is realized using trapezoidal plates. Moreover, the effects of these plates are also evaluated for gain and FBR and the results are shown in Fig. 6(c) and (d), respectively. The value of gain with trapezoidal plates is more stable compered to rectangular plates. Also, the FBR has a satisfactory result using trapezoidal plates. A U-shaped feed structure is adopted between the radiation elements. This simple U-shaped feed structure can well excite the radiation elements by optimizing its width (W1). In the other word, the most appropriate impedance matching is obtained by chosen a suitable width. Hence, different amounts of W1 are analyzed and their effects on S11 and input impedance are illustrated in Fig. 7 (a) and (b), respectively. When W1 decreases from 4 mm to 2 mm, S11 at frequency 2 GHz reaches to 10 dB while the frequencies higher and lower than 2 GHz are almost stable. Also, considering Fig. 7(b) it can be interpreted that these varieties have a relation with input impedance that is relatively changes with
Table 1 Specified dimensions of the presented antenna. Parameters
Lr
L1
L2
L3
L4
L5
L6
L7
Value (mm) Parameters Value (mm)
150 L8 22.9
132 Hr 30
135 H1 42
25 H2 42
50 H3 20
39.3 W1 4
84 h 60
20.4 G 2
Fig. 4. Simulated current distribution at different time phases of 0°, 45°, 90° and 135° for frequencies of 1.9 GHz and 2.1 GHz.
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respect to S11. On the other hand, when W1 increases from 4 mm to 6 mm, the value of S-parameter is significantly increased and the input impedance is decreased and reached to almost 30 X. Simulated radiation patterns of the antenna at xoz-plane and yozplane at frequencies 1.9 GHz and 2.1 GHz are plotted in Fig. 8(a) and (b), respectively. According to these plots, the proposed antenna provides RHCP with a good performance and low cross polarization (LHCP) with values of less than 20 dB at 1.9 GHz and 10 dB at 2.1 GHz. The concept of right-handed circular polarization has already been mentioned in the previous section by the indicated surface current distributions in Fig. 4.
Fig. 5. Simulated results of the proposed antenna with defected side walls, closed side walls and without side walls. (a) S11, (b) axial ratio, (c) gain and (d) FBR.
Fig. 8. Simulated radiation patterns of the proposed antenna at xoz-plane and yoz-plane at (a) 1.9 GHz and (b) 2.1 GHz.
Fig. 6. Simulated results of the proposed antenna with trapezoidal-shaped and rectangular-shaped dipoles. (a) S11, (b) axial ratio, (c) gain and (d) FBR.
Fig. 7. Simulated results of (a) S11 and (b) input impedance for various amounts of W1.
Fig. 9. Implementation of the proposed magneto-electric dipole antenna.
Fig. 10. Measured and simulated results of S11.
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The prototype of the proposed magneto-electric dipole antenna is implemented with copper material and the measurement process of far-filed parameters is conducted in an anechoic chamber. Also, S11 is measured by the Keysight N5242A PNA-X network analyzer. The implementation of the magneto-electric dipole antenna is shown in Fig. 9. The measured and simulated S-parameter of the proposed magneto-electric dipole antenna is illustrated in Fig. 10. As observed in this figure, the measured frequency bandwidth is from 1.4 GHz to 2.8 GHz with S11 < 10 dB while the simulated one is from 1.5 GHz to 2.7 GHz. It is worth noting that the obtained frequency range can be used for GSM1800 (1710–1880 MHz), GSM1900 (1850–1990 MHz), CDMA2000 (1920–2170 MHz), LTE2300 (2300–2400 MHz) and LTE2500 (2500–2690 MHz) services. The measured and simulated axial ratio is also shown in Fig. 11. It can be seen that, the axial ratio bandwidth (ARBW) is less than input impedance bandwidth but, it completely covers the mentioned services. The simulated 3-dB AR bandwidth is 41% from
Table 2 Overall specifications of the proposed antenna. Simulated FC [GHz] S11 [dB] Gain [dBi] FBR [dBi] HPBW [deg] AR [dB]
Fig. 12. Measured and simulated results of gain and FBR.
1.9 29.9 9.1 21.1 67 1.7
2.1 37.1 9.5 21.4 75 2.4
1.9 12 6.2 15.8 60.5 1.8
2.1 14 6.3 18.5 63.5 2.1
Table 3 Comparison between the proposed antenna and previous works. Ref.
BW [GHz]
Gain [dBi]
CP
Size [mm3]
[17] [18] [19] [20] [21] [22] [23]
1.67–2.22 1.88–3.3 1.86–2.96 1.62–2.81 1.83–2.73 1.35–4.2 2.15–3.4 4–6.3 1.4–2.8
9.2 ± 1.1 8.6 ± 0.8 8.1 ± 0.8 >6.6 8.4 ± 0.2 >5.4 >8
U U
152 152 15 112 112 19 130 130 21 120 120 30 150 150 21 150 130 30 100 100 30.3
>6.2
U
150 150 42
This work
Fig. 11. Measured and simulated results of axial ratio.
Measured
1.7 to 2.6 GHz. Also, the measured ARBW has good agreement with the simulated one. Fig. 12 is depicted measured and simulated gain and FBR. As shown in this figure, the measured results are lower than simulated one due to the fabrication errors and environment effectives; however, these results are still satisfactory for practical standards. The measured gain is 6.2 dBi and 6.3 dBi at frequencies 1.9 GHz and 2.1 GHz, respectively. In addition, the measured FBR is 15.8 dB and 18.5 dB at frequencies 1.9 GHz and 2.1 GHz, respectively. Fig. 13(a) and (b) are indicated measured and simulated radiation patterns at xoz-plane. Considering these plots, low differences between the simulated and measured RHCP are observed. The tolerance between the simulated and measured LHCP is impressive, but it is satisfactory result. Also, HPBWs of 60.5° for frequency 1.9 GHz and 63.5° for frequency 2.1 GHz are realized that are appropriate for BTS applications according to required standards of base stations. All measured and simulated results of the proposed magnetoelectric dipole antenna are summarized in Table 2. Moreover, a comparison between the previous magneto-electric dipole antennas [17–23] with the proposed antenna in this article that have approximately same structures and specifications is conducted and the results are indicated in Table 3. It can be concluded that the proposed antenna in this article has wider frequency bandwidth and benefits from CP characteristic and it has simpler structure as well. Despite CP characteristic and wide frequency bandwidth in [22], it has lower gain at frequency range 1.5– 2 GHz compared to the proposed antenna in this article. Also, the proposed CP magneto-electric dipole antenna in [23] has satisfactory performance but it does not cover GSM1800, GSM1900 and CDMA2000 services.
4. Conclusion
Fig. 13. Measured and simulated results of radiation patterns at (a) 1.9 GHz and (b) 2.1 GHz.
A wide-band CP magneto-electric dipole antenna is studied in this article. The proposed antenna consists of a metallic reflector with defected side walls to enhance the gain, FBR and impedance matching as well. The vertical and trapezoidal horizontal plates are utilized to realize magnetic and electric dipoles, respectively. The U-shaped feed structure is employed to excite the magnetoelectric dipole element and also using optimization of its dimensions the wide frequency bandwidth is realized. The mechanism
P. Mohammadi et al. / Int. J. Electron. Commun. (AEÜ) 105 (2019) 92–97
of CP characteristic is analyzed and shown that the trapezoidalshaped electric dipole has the main role to obtain axial ratio of less than 3 dB. According to measured results, the proposed antenna operates at frequency range 1.4–2.8 GHz that can be covered GSM1800, GSM1900, CDMA2000, LTE2300 and LTE2500 services. Considering the operating frequency range, satisfactory HPBW and gain and also a simple structure, the proposed antenna is the proper candidate for femtocell applications due to the GSM, CDMA and LTE services. Conflict of interest The authors declared that there is no conflict of interest.
[9] [10] [11]
[12]
[13]
[14]
Acknowledgment
[15]
The authors would like to acknowledge the Microwave and Antenna Research Center, Urmia Branch, Islamic Azad University, Urmia, Iran for measurement of the proposed antenna.
[16]
[17]
References [1] Jovanovic Predrag, Bjelica Milan. Estimation of GSM base station output power cumulative density function. AEU - Int J Electron Commun 2014;68:717–9. [2] Mitic Dragan, Lebl Aleksandar, Markov Zarko. Influence of traffic model on the calculation of BTS output power in GSM network. AEU - Int J Electron Commun 2015;69:836–40. [3] Choi Woo-Yong. A method for determining the number of Base stations connected to a BSC in CDMA cellular communication systems. AEU - Int J Electron Commun 2002;6:367–72. [4] Itoh Kazuya, Konno Keisuke, Chen Qiang. Shingo Inoue. Design of compact multiband antenna for triple-band cellular base stations. IEEE Antenn Wirel Propag Lett 2015;14:64–7. [5] Najafnezhad Elnaz, Nourinia Javad, Ghobadi Changiz, Majidzadeh Maryam, Mirzamohammadi Farnaz. A high gain dual-band printed antenna for LTE base stations with a corner reflector. AEU - Int J Electron Commun 2018;87:173–9. [6] Rezvani MirHamed, Mohammadi Pejman. Microstrip antenna with aperture reflector and C-shaped dipoles for LTE and wireless communications. AEU - Int J Electron Commun 2018;94:12–8. [7] Govindanarayanan Idayachandran, Rangaswamy Nakkeeran. Asymmetric folded dipole antenna with high front-to-back ratio for LTE base stations. IEEE Antenn Wirel Propag Lett 2015;15:869–72. [8] Rajagopal Senthilkumar, Chennakesavan Gokulnath, Subburaj Deepak Ram Prasath, Srinivasan Raju, Varadhan Abhaikumar. A dual polarized antenna on a novel broadband multilayer artificial magnetic conductor backed surface for
[18] [19] [20]
[21] [22]
[23]
[24]
[25]
[26]
97
LTE/CDMA/GSM base station applications. AEU - Int J Electron Commun 2017;80:73–9. Rezvani M, Mohammadi P. A dual-polarized reflector antenna with k/2 printed dipoles for femtocell applications. J Instrum 2019;14:P02004. Dai Xi-Wang, Zhou Tao. Dual-band reflectarray with crossed-dipole elements for GSM and LTE applications. AEU - Int J Electron Commun 2016;70:605–10. Dai Xi-Wang, Zhou Xiao-Yu, Luo Guo-Qing. Wideband directional antenna system with different polarizations for wireless communication system. AEU Int J Electron Commun 2017;75:119–23. Tejpal Vivekanand Tiwari, Bhatnagar Deepak, Yadav Dinesh, Rawat Sanyog. A dual-band CP dual-orthogonal arms monopole antenna with slanting edge DGS for C-band wireless applications. AEU - Int J Electron Commun 2018;84:251–7. Li Chao, Zhang Fushun, Zhang Fan, Yang Kaiwen. A wideband circularly polarized antenna with wide beamwidth for GNSS applications. Prog Electromag Res C 2018;84:189–200. Choi Eun-cheol, Lee Jae W, Lee Taek-Kyung, Lee Woo-Kyung. Circularly polarized s-band satellite antenna with parasitic elements and its arrays. IEEE Antenn Wirel Propag Lett 2014;13:1689–92. Li Jianxing, Shi Junwei, Li Lumei, Khan Tayyab Ali, Chen Juan, Li Yingsong, Zhang Anxue. Dual-band annular slot antenna loaded by reactive components for dual-sense circular polarization with flexible frequency ratio. IEEE Access 2018;6:64063–70. Li Yingsong, Mittra Raj. A three-dimensional circularly polarized antenna with a low profile and a wide 3-dB beamwidth. J Electromag Waves Appl 2016;30:89–97. Ding Chen, Luk Kwai-Man. Low-profile magneto-electric dipole antenna. IEEE Antenn Wirel Propag Lett 2016;15:1642–4. Ge Lei, Luk Kwai Man. A low-profile magneto-electric dipole antenna. IEEE Trans Antenn Propag 2012;60:1684–9. Ge Lei, Luk Kwai Man. A magneto-electric dipole antenna with low-profile and simple structure. IEEE Antenn Wirel Propag Lett 2013;12:140–2. Govindanarayanan Idayachandran, Rangaswamy Nakkeeran, Anbazhagan Rajesh. Design and analysis of broadband magneto-electric dipole antenna for LTE femtocell base stations. J Comput Electron 2016;15:200–9. Luk Kwai-Man, Biqun Wu. The magnetoelectric dipole—a wideband antenna for base stations in mobile communications. Proc IEEE 2012;100:2297–307. Feng Chao-Qiang, Zhang Fu-Shun, Zhang Han-Jing, Jun-Xiu Su. A single-feed circularly polarized magnetoelectric dipole antenna for wideband wireless applications. Prog Electromag Res M 2018;65:1–8. Tao Jun, Feng Quanyuan. Dual-band magnetoelectric dipole antenna with dual-sense circularly polarized character. IEEE Trans Antenn Propag 2017;65:5677–85. Feng Botao, Lia Shufang, An Wenxing, Hong Weijun, Wang Shuai, Yin Sixing. A printed dual-wideband magneto-electric dipole antenna for WWAN/LTE applications. AEU - Int J Electron Commun 2014;68:926–32. An Wen Xing, Wong Hang, Lau Ka Leung, Li Shu Fang, Xue Quan. Design of broadband dual-band dipole for base station antenna. IEEE Trans Antenn Propag 2012;60:1592–5. Li Zuming, Sun Yufa, Yang Ming, Zhifeng Wu, Tang Peiquan. A broadband dualpolarized magneto-electric dipole antenna for 2G/3G/LTE/WiMAX applications. Prog n Electromag Res C 2017;73:127–36.