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A Compact Switched Beam Antenna Array for ISM Band
Nguyen Tri, Bui Thi Duyen, Hoang Thi Phuong Thao*
Abstract—This paper proposes the switched beam antenna array at the center frequency of 2.45GHz with a bandwidth of 187MHz, from 2.32GHz to 2.51GHz for the ISM band. The phase shifter of antenna utilizes a 4 X 4 planar Butler matrix with phase differences between its outputs of ±135° and ±45° to obtain four the different main beam directions. The proposed design is fully described including the patch antenna element, the antenna array, the phase shifter that forms the completed antenna array. The antenna array achieves a gain max up to 7dBi, and the angles of the main beam directions of —41°, -12°, +15°, +48° in a horizontal plane. The beamwidth of the four main beams is from 26° to 31.8° in E-plane and from 38.50ot0 54.4° in H-plane. The advantage of the antenna is the planar structure and compact dimension of 200x230mm2.
The antenna simulation and optimization are performed using CST Microwave studio.
Index Terms—Internet of Things, Clustering, Wireless Sensor Networks, Pervasive Computing.
1. Introduction
I
N recent years, switched beam antenna arrays (SBAA) have been widely used in many applications such as 5G mobile telecommunication [1-3], satellite communication [4-6], WiFi-based indoor positioning systems (IPSs) [7-10], and other wireless communication sys
tems to achieve desired radiation pattern and high gain [11]. There have been many publications of SBAA with significant achievements over the last dedicates [12- 16]. However, the challenge in designing the steering antenna array is obtaining optimization in various con
straints such as including gain, size, high complexity, and other parameters.
This paper proposes the SB A A at 2.45GHz for IPSs.
The antenna consists of a phase-shifter and an antenna array designing on R04003C substrate. The phase
shifter bases on a 4x4 Butler matrix, and the antenna array is composed of the four proposed patch antennas with a total dimension of 1.6x1.8mm2 and planar struc
ture. The beam of SBAA can alter in four directions with sweep angles of -41°, -12°, +15°, +48° and the gains of from 4.07 to 7.19dBi. The contribution in this work is that the BSAA obtains a good optimization between the parameters such as gain, simplicity of structure, and beamwidth. The rest of the paper is organized as follows. Section 2 presents the SBAA design. Section 3 describes the antenna results and discussions. The
Nguyen Tri is with Control, Automationin Productionand Improve
ment of Technology Institute,Vietnam.
Bui Thi Duyen, Hoang Thi Phuong Thao are with Faculty of Automation Technology, Electric Power University, Vietnam (E-mail:
Corresponding author: Hoang Thi Phuong Thao (e-mail:
Manuscriptreceived April 04,2021; revisedMay 11, 2021;acceptedJune 10, 2021.
Digital Object Identifier10.31130/ict-ud.2021.134
conclusion is presented in the last section.
2. Antenna design
The antenna array consists of a phase shifter basing on the Butler matrix, and an antenna array with four patch antenna elements with detailed description as below sub-section.
Fig. 1:The structure of thebeamsteeringantenna
2.1. Patch antenna element
The proposed element is a patch antenna operating at a center frequency of 2A5GHz showing in Figure 2.
The antenna element is designed, simulated using CST software, and fabricated on R04003C substrate with er — 3.55 and h = 0.8mm. The initial structure of the antenna element is a conventional patch with an overall dimension of 66 X 66mm2. Then, two opposing corners of the radiation patch were charmed with an angle of 45°
to archive Circular Polarity (CP). The feeding is blended into the view side for improving the CP. The antenna element's dimensions are shown in Table 1.
Figure 3 shows the simulated reflection coefficient of the patch antenna. It shows that the antenna operates at a frequency of 2A5GHz with a —lOdB bandwidth of
ISSN 1859-1531
2 UD - JOURNAL OF SCIENCE AND TECHNOLOGY: ISSUE ON INFORMATION AND COMMUNICATIONS TECHNOLOGY, VOL. 19, NO. 6.2, 2021
110MHz. The simulated peak gain is 6.58dBi as shown in Figure 4. The antenna achieves a CP with a good axial ratio of less than 3dB in the wide CP as shown in Figure 5.
TABLE 1: The parameters ofthe proposedantennaelement Parameter w s w b wp c Lfi W’/I L/2 w>2
Value(?nn?) 66.0 31.1 3.0 19.5 4.5 16.0 3.0
Fig.2: The proposedCP Antenna element structure
Frequency/GHz
Fig. 3: The simulated reflection coefficient ofpatch element
Fig. 4: Simulated 3D radiationpattern of the proposed element
30
0
/ 330
240 ---300 270
Fig. 5: Simulated radiation pattern in E-plane and H-planeofthe proposedantenna
2.2. Phase shifter design
The model of the phase shifter is a 4x4 Butler matrix with four input ports, from 1 to 4, and four out ports, from port 5 to 8 as shown in Figure 9. Power from the outputs of the matrix with phase differences between is feed to four the patch antenna elements to control the direction of the antenna beam. The phase difference between the outputs of Nx N Butler matrix is according to the equation (1):
A<p=±^i X 180° (1)
where N is beam number and N — 2l with I = 1.2,3... In 4x4 Butler matrix, N = 4, Ad =
±45; ±135°.
The matrix consists of two classes with two 90°
hybrid couplers and two fixed phase shifters for each.
A cross over is used to connect two the classes and another one connects the second class to the output ports 6 and 7.
Nguyen Tri eta!:. A COMPACT SWITCHED BEAM ANTENNA ARRAY FOR ISM BAND 3
2.2.1. Hybrid coupler
The hybrid coupler is a conventional 90° shifter. Its purpose is to divide input power into two equal parts in its output ports and to provide a 90° phase difference between them. The signal feeding to port 1 is divided equally to port 2 and port 3 and isolated to port 4. The design of the coupler is shown in Figure 7 with its size of 22 X 22mm2.
Xg/4
Port 3 o ' o Port 4
Ầợ /4
Port 1 • ° Port 2
Fig.7: Structure of the hybridcoupler
Output
Port 1 Port 2 Port3 Port 4 Input
Fig. 9: The 4x4 Butler matrix structure
The simulated results of s parameters are plotted in Figure 10. The antenna archives a good resonance with a minimum reflection coefficient of appropriately -40dB at 2AGHz. The -lOdB bandwidth of the matrix archives 500MHz, from 2.2GHz to 2.7GHz.
2.2.2. Crossover
The structure and dimension of the crossover are presented in figure 8. Its purpose is to cross two trans
mission lines to connect the hybrid coupler to the phase shifter with minimum coupling.
After that, the 4x4 Butler matrix uses 45° and 180°
fixed phase shifter corresponding to 3x(A/4) and A/2 microstrip lines.
Fig.8: Crossover design at2.45GHz
Port 3
2.2.3. Full phase shifter
The completed phase shifter is a Butler matrix con
sisting of the hybrid coupler, the crossovers, and the fixed phase shifters mentioned above Figure 9 shows the Butler matrix with its dimension of 147 x188mm2.
A signal is a feed to one of four input ports, namely 1, 2, 3, 4, by the radio frequency switch circuit, then it is transmitted to the output ports from 5 to 8.
Fig. 10: The simulated reflection coefficient of each port of the Butlermatrix
2.3. Switched beam antenna array
The proposed steering linear antenna array com
poses three parts including a Butler matrix, and an antenna array as shown in Figure 11. Four output ports of the Butler matrix are connected to the feeding ports of four antenna elements. The radio frequency switch can switch a feeding signal to one of four input ports of the 4 x4 Butler matrix. The change of the active input port of the matrix leads to the steering of beam direction. The antenna array consists of four patch antenna elements placing side by side with the center-to-center space
4 UD - JOURNAL OF SCIENCE AND TECHNOLOGY: ISSUE ON INFORMATION AND COMMUNICATIONS TECHNOLOGY, VOL. 19, NO. 6.2. 2021
between adjacent elements of A0/2, 60 mm. The total dimension of the proposed steering linear antenna array is 230x200mm2.
230 mm
Fig. 11: Structure of the switched beam antenna array
The output signal feeding to four antenna elements provides the different beam direction corresponding to one of four exciting ports as shown in Figure 11. The main beam 6 angle is given by the equation (2)
0=arccosf (2)
where k = 2tt/A, d is the distance between antenna elements, and A is the wavelength.
3. Results and Discussion
Frequency |GHz|
Fig. 12:The simulated reflection coefficient of each portof the Butlermatrix
Figure 12 shows the simulated S-parameters of the proposed steering antenna array. It operates at the center frequency of 2A5GHz with a bandwidth of 187AIHz, from 2.32GHz to 2.52GHz. The polar and 3D radiation patterns are plotted in figure 13. It shows that the antenna array achieves peak gains of 7 AOdBi, 7.04dBi, 4.07dBi, 4.7dBi at four main beam directions, and the angles of four main beams are from 26° to 31.8°
in E-plane and from 38.5 to 55.4° in H-plane. The angles of the main beam directions are —41°, —12°, +15° to +48° in a horizontal plane.
Table 2 summarizes the performance of the proposed antenna. The antenna has a compact size and obtains a high gain, a narrow sweep angle in several directions.
Although our contribution is not outstanding, the pro
posed antenna achieves a balance in the parameters mentioned in Table 2. Besides, the antenna element achieves a CP, which helps to reduce the multipath ef
fect, energy loss, and Faraday rotation effect in wireless communications.
TABLE2: Performance summary of the proposed BSAA Sweep
angle
-41°, -12°;
+15 ,+48°
Side lobe level(dB)
-9.0 +-4.0 Beamwidth
E-plane (°)
31.8; 26;
25.3; 34.3
Substrate RO 4003C
Beamwidth H-plane(°)
—38.5+55.4 Structure Planar Peak gain
(dBi)
4.07 + 7.19 Polarity of antenna element
Planar Bandwith
(MHz)
187 Dimension Ao 1.6x1.8
Fig. 13: The 3D Radiation pattern of the switchedbeamantenna array
4. Conclusion
A SBAA using 4x4 Butler matrix is pro
posed with its beam steering at four directions in
—41°,—12°.+15°,+48° in a horizontal plane with a gain of from 4dBi to 7dBi. The antenna operates at 2A5GHz with a bandwidth of 187MHz. It has a com
pact structure, high gam, narrow sweep angle that is suitable for the ISM band or IPSs based WiFi based 802.11 a/n/ac standards. In the future, the antenna will be fabricated and measured to verify the simulated results.
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Nguyen Tri graduated in the field of In
strumentation and Industrial Informatics in 2004 at Hanoi University of Science and Technology. He completed the master’s de
gree in Automation in 2015 at Military Tech
nical Academy. Since 2005. Nguyen Tri is researcher at the Control, Automation in Production and Improvement of Technology Institute, Academy of Military Science and Technology. His research interest concerns Signal Processing, Laser Tracking System, Design of embedded systems for control and automation systems.
Bui Thi Duyen graduated in the field of Instrumentation and Industrial Informatics In 2004 and completed the master’s degree in Control Engineering and Automation in 2007 at Hanoi University of Science and Technology. She is a PhD in Control and Automation Engineering, majoring in Mea
surement at Hanoi University of Science and Technology in 2020. Since 2005, Thi Duyen Bui is working as a lecturer at the Faculty of Automation Technology, Electric Power University. At present, Thi Duyen Bui’s main research areas are antennas and high-frequency circuits, wireless communication, indoor localization system, metamaterials, and design of embed
ded systems for control and automation systems.
Hoang Thi Phuong Thao received the Dipl, of Engineer (2004), Master of Science (2007), and PhD degree (2019) in Electron
ics and Telecommunications from Hanoi University of Science and Technology, Viet
nam. Currently, she is a lecturer at Elec
tronics and Telecommunications Faculty, Electric Power University, Vietnam. Her re
search interests are antenna design, high- frequency circuits, metamaterials, wireless communication, and localization systems.
She has had serveral publicattions in the ISI, Scopus jounals and international conferences in antenna and wireless communication field. She has a total 15 years of experience in teaching and researching.
