- Email: [email protected]
Design, fabrication and measurement of triple band frequency reconfigurable antennas for portable wireless communications
Accepted Manuscript Regular paper Design, Fabrication and Measurement of Triple Band Frequency Reconfigurable Antennas for Portable Wireless Communications Sadiq Ullah, Shahzeb Hayat, Anees Umar, Usman Ali, Farooq A Tahir, James A Flint PII: DOI: Reference:
S1434-8411(17)31478-4 http://dx.doi.org/10.1016/j.aeue.2017.07.028 AEUE 51985
To appear in:
International Journal of Electronics and Communications
Received Date: Revised Date: Accepted Date:
14 June 2017 20 July 2017 25 July 2017
Please cite this article as: S. Ullah, S. Hayat, A. Umar, U. Ali, F.A. Tahir, J.A. Flint, Design, Fabrication and Measurement of Triple Band Frequency Reconfigurable Antennas for Portable Wireless Communications, International Journal of Electronics and Communications (2017), doi: http://dx.doi.org/10.1016/j.aeue.2017.07.028
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Design, Fabrication and Measurement of Triple Band Frequency Reconfigurable Antennas for Portable Wireless Communications Sadiq Ullaha,*, Shahzeb Hayatb, Anees Umara, Usman Alia, Farooq A Tahir c, James A Flintd a
Department of Telecommunication Engineering, UET Peshawar, Mardan, 23200, Pakistan b
c
Department of Biomedical Engineering, Ulsan University, 44610, South Korea
Research Institute for Microwave and Millimeter-wave Studies (RIMMS), National University of Sciences and Technology (NUST), Islamabad, 44000, Pakistan
d
School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University,
Leicestershire, LE11 3TU, UK
*
Corresponding Author:
Email Address: [email protected]
Abstract In this paper two triple-band monopole antennas are proposed for portable wireless applications such as WiFi, WiMAX and WLAN. Two different geometrical structures are used for the radiating elements of these antennas, each
printed on a low cost FR-4 substrate. Truncated metallic copper ground is used to attain optimum radiation pattern and better radiation efficiency. The frequency of the antennas is reconfigured using a lumped-element switch. The proposed antennas covers three frequency bands 2.45, 3.50 and 5.20 GHz depending upon the switching conditions. Both antennas works with an optimum gain (1.7-3.4 dB), bandwidth (6-35%), VSWR (<1.5) and radiation efficiency (85-90%). Due to its affordable size (1.6×35×53 mm3), the antennas can be used in modern and portable communication devices such as laptops, iPads and mobile phones. The prototype of the antennas are fabricated and the measurements and simulations are found in close agreement. Keywords: Triple band, Monopole, WiMAX, WLAN, Portable devices 1. Introduction The modern telecommunication industry has been developed according to the growing needs of customers required in smart devices. These devices are capable of running more than one application at a time in contrast to their earlier counterparts. Each application has its own operation frequency band, i.e. Global Positioning System (GPS), Wireless Fidelity (Wi-Fi), Global System for Mobile Communication
(GSM),
Bluetooth
and
Worldwide
Interoperability
for
Microwave Access (WiMAX). Integrating separate antenna for each application makes the device larger in size and unpleasant. Hence a single antenna capable of operating at different frequency bands is the key requirement of modern devices.
To fulfill this requirement, researchers proposed wideband and multiband antennas [1-4]. A 56×59 mm2, antenna is reported in [1] for triple band applications (1.576 GHz, 2.668 GHz and 3.636 GHz). In [2] a relatively larger size (90×50 mm2) dualband antenna was designed for Industrial Scientific and Medical (ISM) band applications (2.45 GHz and 5.2 GHz). In [3, 4] dual band antennas of reasonable dimensions were reported for 2.4 GHz and 5 GHz applications. A 58×62 mm2 large antenna was presented in [5] for GSM and Wireless Local Area Networks (WLAN) applications. Some recently proposed approaches for the design of multiband antennas include integration of a metamaterial inspired split ring structure [6] and slots [7] within the radiating element to obtain resonance in WLAN (2.45 GHz, 5.2 GHz), WiMAX (3.5 GHz) and Wave (5.9 GHz) frequency bands. Defective ground planes [8] are also proposed to get wide and dual band response in WLAN and WiMAX frequency bands. Beside its advantages of compact size and simplicity, multiband and wideband antennas have some limitations due to their static frequency response. In other words a multiband/wideband antenna cannot be tuned to a specific frequency band/bands according to user demands. Alternatively, these antennas radiates all of its designed frequency bands without any flexibility to select or suppress a particular frequency band, which can lead to more power consumption and co-channel interference in neighboring devices. To address this problem, reconfigurable antennas are a better choice.
The packing of more than one functionality in single device made the design of reconfigurable antenna as an active topic of research for the antenna and microwave engineers across the globe. This is because of the reason that the important characteristics of the reconfigurable antenna such as radiation pattern, polarization and frequency of the operation can be changed dynamically through the use of the external control, and provides flexibility to the system [9]. Comparing with the multiband and wideband antenna, a frequency reconfigurable antenna has tendency to operate at user desired frequency band, without disturbing other bands of the antenna, and making efficient use of the frequency spectrum [10]. Reconfigurability in antenna system can be achieved using various methods and techniques, such as by inserting slots and switches in the radiating element of an antenna [11, 12]. Reconfigurability of an antenna is actually the disturbing or changing of the current distribution or flow, which can be accomplished by using numerous switching methods such as Radio Frequency (RF) switches, Micro-Electro-Mechanical Systems (MEMS) switches, varactors or PIN diodes and tunable materials [13]. Different geometrical shapes [14-17] have been proposed for designing reconfigurable antennas. A dual band antenna of relatively reasonable size (40×40 mm2) is presented in [18]. This antenna works in WLAN (2.45 GHz) and WiMAX (3.5 GHz) bands and is reconfigured using two pin diodes and external capacitors. In [19] a triple band (5.3, 5.8 and 7.2 GHz) antenna occupying an
overall volume of 3925 mm3 is designed and reconfigured using pin diode switches. The antenna lacks the ability to radiate omni-directionally and does not cover the WiMAX band. A pin-diode controlled antenna, covering 2.45, 3.5 and 5.2 GHz frequency bands is presented in [20]. The antenna is comparatively larger in size (83.1×47 mm2) and radiates with a relatively lower gain (<3 dB). In this work, two relatively compact and efficient planar reconfigurable antennas, has been designed and fabricated. The proposed antennas work in either single or dual frequency modes with an adequate gain, depending on the status of the lumped-element switch installed in the radiating patch. The subsequent sections of the paper are organized as follows: Section 2 explains the geometry and design theory of the proposed, i.e. Nine and Epsilon shaped antennas. Measured and simulated results are compared and discussed in section 3. The paper is concluded in section 4. 2. Design and Relevant Theory This part presents theory and design procedure of the proposed antennas. Fig. 1 present the layout of the proposed ‘nine’ and ‘epsilon’ shaped reconfigurable antennas. The radiating element is printed on a low cost and easily available FR-4 substrate, having a relative permittivity and loss tangent of 4.3 and 0.02, respectively. The substrate is backed by a truncated metallic ground plane to obtain better efficiency, gain and bandwidth. The designed antennas are excited
using a 3 mm wider microstrip line with a characteristic impedance of 50 ohms. In order to excite the antennas; a waveguide port is assigned to the microstrip line. A slot of 1 mm width is reserved in the radiating element of the antenna to incorporate the switch (SW) at the right position. The net dimension of the proposed antennas are 35×53×1.6 mm3. The effective resonant length of the antennas for a specific resonant frequency (fr) is calculated using the well-known transmission line theory [21]: (1)
Where, c is the speed of light equal to 3×108 ms-1 , εr is relative permittivity of the substrate and h is the thickness of the substrate. The various dimensions of the
Ant1
antennas are listed in Table 1.
Y
Z X
Ant2
SW
Front view
Rear view
Figure 1: Various geometrical views of the proposed antennas Table 1: Dimensions of the proposed antennas Length
D1 D2 D3 D4 D5 Df Ds Dw W
Ant1 Value (mm) 7
3
5
4
6
18 40
Length
L2
Ls
Lg
r1
r2
2.5 40
13
8
10 20
L1
35
S1 S2
3 W2
Ant2 Value (mm) 17
12
5.9
3. Results In this section the performance matrices (gain, reflection coefficient, and surface currents) of the two antennas are discussed. The simulations are performed using the CST MWS (2015). The antennas were fabricated using a cheaper FR-4 substrate (Fig. 2). The measurements are performed using a Vector Network Analyzer (VNA) and anechoic chamber at National University of
Science and Technology (NUST) Islamabad. The antennas works in a dualband and single band modes when the switch (SW) is turned ON and OFF respectively (Table 2). For the proof of concept the switch is turned ON by using a shorting wire across the gap reserved for the switch. It is turned OFF when the gap is left open. By altering the state of the switch the proposed antenna operates in single band (3.50 GHz) and dual band (2.45 and 5.20 GHz) modes. Table 2: Switching modes for Ant1 and Ant2 Switch status
Frequency band (GHz)
1. Dualband
ON
2.45 and 5.20
2. Single band
OFF
3.50
Ant2
Ant1
Mode
Front view
Rear View
Figure 2: Different views of the fabricated antennas 3.1. Reflection coefficient (S11) The two antennas operates in a frequency mode 1, when switch (SW) is turned ON. In this frequency mode it give resonance at the lower (2.45 GHz) and upper (5.2 GHz) bands (Fig. 3a). When the switch (SW) is in off condition, the antennas work in the single-band mode at 3.5 GHz (Fig. 3b).
(a)
(b)
Figure 3: Simulated and measured reflection coefficient of the proposed antennas (a) Switch ON (b) Switch OFF Both antennas give a significant amount of driving point impedance bandwidth (S11<-10 dB) in all the three frequency bands. I.e. a bandwidth of (13.5%, 35.72% and 9.94%) and (14.46 %, 27.07 %. and 6.15 %) at 2.45, 3.50 and 5.20 GHz, is attained by the Ant1 and Ant2, respectively. 3.2. Radiation patterns and current distribution The simulated and measured gain patterns of the proposed antennas in the Eplane (YZ, ϕ=900) and H-plane (XZ, ϕ=00) at 2.45, 3.5 and 5.2 GHz are portrayed in Fig. 4. The radiation patterns of the two antennas have been measured in the anechoic chamber (Fig. 5). The Ant1 gives a peak gain of 1.7 dB at 2.45 GHz, 2.5 dB at 3.5 GHz and 3.4 dB at 5.2 GHz. Ant2 gives a maximum gain of 1.92 dB, 2.57 dB and 3.01 dB at 2.45, 3.5 and 5.2 GHz, respectively. The antenna radiates omni-directionally in the H-plane for all the three frequency bands. A ‘Figure of eight’ shape radiation pattern is achieved in the E-plane at 2.45 and 3.5 GHz with a null located at θ= 900. At 5.2 GHz the location of null lobe for Ant1 has been shifted to θ= 600 in the E-plane. The measured and simulated gain patterns were found to be in reasonable agreement both principal planes. Both antennas function efficiently with a radiation efficiency>85 % in the desired frequency bands.
2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 4: Simulated and measured gain patterns in both principal planes The distribution of the surface currents of the proposed antennas at 2.45, 3.50 and 5.20 GHz are illustrated in Fig. 6. The segments of the radiating element where the surface current density is maximum and which primarily contributes in generating a given frequency band are encircled in the figure. In Ant1, the loop in the 9-shape and vertical segment below the switch position shows maximum current density to generate the 2.45 GHz band. The current density is prominent below the switch position in Ant1 to give resonance at 3.5 GHz. The loop of the 9-shape radiating element is disconnected in this off-switch frequency mode.
Probe (Horn Antenna) Antenna Under Test (Ant2)
Positioner
Probe (Horn Antenna)
Antenna Under Test (Ant1)
Positioner
Figure 5: Measurement setup of Ant1 and Ant2 in anechoic chamber
The current distribution is maximum across the loop segment of Ant1 to generate the upper frequency band (5.2 GHz). In Ant2 the entire epsilon segment and some part of the feedline shows maximum current density to generate the lower frequency band of 2.45 GHz. The lower part of the epsilon shape segment shows higher current density below the switch position to give resonance at 3.5 GHz. The upper part of the epsilon segment is disconnected in this off-state switching mode and hence does not contribute in generating this frequency mode. To generate the upper frequency band of 5.2 GHz, the epsilon-shape segment of Ant2 is excited for maximum current density. 2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 6: Surface current plots of the proposed antennas at different frequency bands
4. Conclusion In this paper two antennas of reasonable size, have been designed, fabricated, measured and validated. The proposed antennas works in different frequency modes, depending on the switch position. I.e. the antennas operates in dual frequency mode when the switch is turned ON. In contrast, when the switching state is in OFF mode, the designed antennas works in single frequency mode. The simulated results are found in close agreement with the measured results. Both the monopole antennas give an acceptable gain (1.7-3.4 dB), efficiency (85-90%) and bandwidth (6-35%), in the desired frequency bands for a given switching state. The monopoles have an omni-directional pattern in the H-plane. The antennas have an affordable size which enable them to be easily integrated in portable devices such as laptops, tablets and mobile phones.
Acknowledgements The authors of the manuscript thankfully acknowledge, National University of Sciences and Technology (NUST), Islamabad, Pakistan for its support in the required measurements at Research Institute for Microwave and Millimeter-wave Studies (RIMMS). We wish to thank Dr. James Flint of Loughborough University, United Kingdom, for his useful suggestions in modelling of the proposed antennas. We are especially thankful to BOASAR, UET Peshawar for funding this research.
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Raweshidy, D. Budimir., A reconfigurable H-shape antenna for wireless applications., IEEE Conference on Antennas and Propagation (EuCAP) (2010) 1-4. [16]
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2.4/5.2 GHz dual-band WLAN operations., IEEE Transactions on Antennas and Propagation 51 (2003) 2187-2192. [17]
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[20] Idris,
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New York: J. Wiley & Sons, 2016.
Sadiq Ullah is Assistant Professor and Head of Telecommunication Engineering Department, University of Engineering & Technology, Peshawar, Pakistan. Sadiq Ullah received B.Sc. Electrical Engineering from University of Engineering and Technology, Peshawar, Pakistan. He achieved his M.Sc. in Electrical Engineering from University of Engineering and Technology Taxila, Pakistan. In 2007, he joined the Department of Electronic and Electrical Engineering, at Loughborough University, U.K., and was awarded Ph.D. for his research in the field of design and measurement of metamaterial based antennas in 2010. He worked as an Assistant Manager (Electronics) in a public sector R and D organization in Islamabad, where his main responsibilities were hardware, software co-design, designing and testing of high precession electronics, test equipment. His research mainly focuses on design and measurement of low-profile antennas on electromagnetic Bandgap structures, RFID tag antennas and wearable antennas. He has been worked as a Research Associate at Loughborough University, where he researched on the propagation effects of rain, snow, ice, fog and forest in millimeter wave band. During his Ph.D., he published his research in international conferences and journals. ORCID: http://orcid.org/0000-0002-5299-1577 E-mail: [email protected] Shahzeb Hayat is a research student in the Department of Biomedical Engineering, Ulsan University, South Korea. His research interests include planar antenna, millimeter wave antennas, multi band antennas, implanted antennas, Specific Absorption Rate analysis, Frequency Selective Surfaces and EBGs.
Anees Umar is a research student in UET Peshawar, Pakistan in the Department of Telecommunication Engineering, UET Peshawar (Mardan Campus), Pakistan. Currently he is doing research on reconfigurable antennas. His research interests include, planar antennas, millimeter wave antennas and metamaterial surfaces. Usman Ali received his B.Sc. Telecommunication Engineering from University of Engineering and Technology, Peshawar, Pakistan in 2012. He received his M.Sc. in Telecommunication Engineering from University of Engineering and Technology Peshawar, Pakistan in 2017. His research interests include metamaterials, signal processing, Electromagnetic Bandgap structures and wearable antennas. Currently he is working as a Lab Engineer in the same Department. Farooq Ahmad Tahir was born in Faisalabad, Pakistan. He received BE degree in Electrical Engineering from University of Engineering and Technology Lahore, Pakistan in 2005. In 2008, He was awarded Master’s Degree in Radio Frequency Telecommunications and Microelectronics (TRFM) from the University of Nice, Sophia Antipolis, France. During his PhD, his research was focused on “Electromagnetic Modeling, Design and Implementation of Printed Electronically Reconfigurable Reflect array Antenna Systems for LEO Satellites”. This Research was carried out under European Space Agency (ESA), Thales Alenia Space, and French Research Agency. He received Doctorate degree in September 2011 from National Polytechnique Institute of Toulouse (INPT), University of Toulouse, France. His PhD thesis was nominated for Best Thesis Prize for the year 2011 at National Polytechnique Institute of Toulouse, France. Currently he is Assistant Professor in Research Institute for Microwave and Millimeter-wave Studies (RIMMS), National University of Sciences and Technology (NUST), Islamabad, Pakistan James Flint is Reader in Wireless Systems Engineering, Head of the Communications Research Division within the School of Mechanical, Electrical and Manufacturing Engineering. His research focuses on various aspects of wireless systems, especially in the area of transducer design in electromagnetic and acoustics. He has a keen interest in biomimetics, ultrasound and on
converting systems found in nature into workable engineering solutions. Dr Flint was previously employed in the automotive industry and maintains an interest in safety-critical systems, installed performance of antennas and electromagnetic compatibility. In recent years Dr Flint has had a particular interest in band gap structures (both electromagnetic and acoustic).
Figure Captions: Figure 2: Various geometrical views of the proposed antennas Figure 2: Different views of the fabricated antennas Figure 3: Simulated and measured reflection coefficient of the proposed antennas (a) Switch ON (b) Switch OFF Figure 4: Simulated and measured gain patterns in both principal planes Figure 5: Measurement setup of Ant1 and Ant2 in anechoic chamber Figure 6: Surface current plots of the proposed antennas at different frequency bands
Ant1 Y
Z X
Ant2
SW
Front view
Rear view
Figure 3: Various geometrical views of the proposed antennas
Ant1 Ant2
Front view
Rear View
Figure 2: Different views of the fabricated antennas
(a)
(b) Figure 3: Simulated and measured reflection coefficient of the proposed antennas (a) Switch ON (b) Switch OFF
2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 4: Simulated and measured gain patterns in both principal planes
Probe (Horn Antenna) Antenna Under Test (Ant2)
Positioner
Probe (Horn Antenna)
Antenna Under Test (Ant1)
Positioner
Figure 5: Measurement setup of Ant1 and Ant2 in anechoic chamber
2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 6: Surface current plots of the proposed antennas at different frequency bands
S1434-8411(17)31478-4 http://dx.doi.org/10.1016/j.aeue.2017.07.028 AEUE 51985
To appear in:
International Journal of Electronics and Communications
Received Date: Revised Date: Accepted Date:
14 June 2017 20 July 2017 25 July 2017
Please cite this article as: S. Ullah, S. Hayat, A. Umar, U. Ali, F.A. Tahir, J.A. Flint, Design, Fabrication and Measurement of Triple Band Frequency Reconfigurable Antennas for Portable Wireless Communications, International Journal of Electronics and Communications (2017), doi: http://dx.doi.org/10.1016/j.aeue.2017.07.028
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Design, Fabrication and Measurement of Triple Band Frequency Reconfigurable Antennas for Portable Wireless Communications Sadiq Ullaha,*, Shahzeb Hayatb, Anees Umara, Usman Alia, Farooq A Tahir c, James A Flintd a
Department of Telecommunication Engineering, UET Peshawar, Mardan, 23200, Pakistan b
c
Department of Biomedical Engineering, Ulsan University, 44610, South Korea
Research Institute for Microwave and Millimeter-wave Studies (RIMMS), National University of Sciences and Technology (NUST), Islamabad, 44000, Pakistan
d
School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University,
Leicestershire, LE11 3TU, UK
*
Corresponding Author:
Email Address: [email protected]
Abstract In this paper two triple-band monopole antennas are proposed for portable wireless applications such as WiFi, WiMAX and WLAN. Two different geometrical structures are used for the radiating elements of these antennas, each
printed on a low cost FR-4 substrate. Truncated metallic copper ground is used to attain optimum radiation pattern and better radiation efficiency. The frequency of the antennas is reconfigured using a lumped-element switch. The proposed antennas covers three frequency bands 2.45, 3.50 and 5.20 GHz depending upon the switching conditions. Both antennas works with an optimum gain (1.7-3.4 dB), bandwidth (6-35%), VSWR (<1.5) and radiation efficiency (85-90%). Due to its affordable size (1.6×35×53 mm3), the antennas can be used in modern and portable communication devices such as laptops, iPads and mobile phones. The prototype of the antennas are fabricated and the measurements and simulations are found in close agreement. Keywords: Triple band, Monopole, WiMAX, WLAN, Portable devices 1. Introduction The modern telecommunication industry has been developed according to the growing needs of customers required in smart devices. These devices are capable of running more than one application at a time in contrast to their earlier counterparts. Each application has its own operation frequency band, i.e. Global Positioning System (GPS), Wireless Fidelity (Wi-Fi), Global System for Mobile Communication
(GSM),
Bluetooth
and
Worldwide
Interoperability
for
Microwave Access (WiMAX). Integrating separate antenna for each application makes the device larger in size and unpleasant. Hence a single antenna capable of operating at different frequency bands is the key requirement of modern devices.
To fulfill this requirement, researchers proposed wideband and multiband antennas [1-4]. A 56×59 mm2, antenna is reported in [1] for triple band applications (1.576 GHz, 2.668 GHz and 3.636 GHz). In [2] a relatively larger size (90×50 mm2) dualband antenna was designed for Industrial Scientific and Medical (ISM) band applications (2.45 GHz and 5.2 GHz). In [3, 4] dual band antennas of reasonable dimensions were reported for 2.4 GHz and 5 GHz applications. A 58×62 mm2 large antenna was presented in [5] for GSM and Wireless Local Area Networks (WLAN) applications. Some recently proposed approaches for the design of multiband antennas include integration of a metamaterial inspired split ring structure [6] and slots [7] within the radiating element to obtain resonance in WLAN (2.45 GHz, 5.2 GHz), WiMAX (3.5 GHz) and Wave (5.9 GHz) frequency bands. Defective ground planes [8] are also proposed to get wide and dual band response in WLAN and WiMAX frequency bands. Beside its advantages of compact size and simplicity, multiband and wideband antennas have some limitations due to their static frequency response. In other words a multiband/wideband antenna cannot be tuned to a specific frequency band/bands according to user demands. Alternatively, these antennas radiates all of its designed frequency bands without any flexibility to select or suppress a particular frequency band, which can lead to more power consumption and co-channel interference in neighboring devices. To address this problem, reconfigurable antennas are a better choice.
The packing of more than one functionality in single device made the design of reconfigurable antenna as an active topic of research for the antenna and microwave engineers across the globe. This is because of the reason that the important characteristics of the reconfigurable antenna such as radiation pattern, polarization and frequency of the operation can be changed dynamically through the use of the external control, and provides flexibility to the system [9]. Comparing with the multiband and wideband antenna, a frequency reconfigurable antenna has tendency to operate at user desired frequency band, without disturbing other bands of the antenna, and making efficient use of the frequency spectrum [10]. Reconfigurability in antenna system can be achieved using various methods and techniques, such as by inserting slots and switches in the radiating element of an antenna [11, 12]. Reconfigurability of an antenna is actually the disturbing or changing of the current distribution or flow, which can be accomplished by using numerous switching methods such as Radio Frequency (RF) switches, Micro-Electro-Mechanical Systems (MEMS) switches, varactors or PIN diodes and tunable materials [13]. Different geometrical shapes [14-17] have been proposed for designing reconfigurable antennas. A dual band antenna of relatively reasonable size (40×40 mm2) is presented in [18]. This antenna works in WLAN (2.45 GHz) and WiMAX (3.5 GHz) bands and is reconfigured using two pin diodes and external capacitors. In [19] a triple band (5.3, 5.8 and 7.2 GHz) antenna occupying an
overall volume of 3925 mm3 is designed and reconfigured using pin diode switches. The antenna lacks the ability to radiate omni-directionally and does not cover the WiMAX band. A pin-diode controlled antenna, covering 2.45, 3.5 and 5.2 GHz frequency bands is presented in [20]. The antenna is comparatively larger in size (83.1×47 mm2) and radiates with a relatively lower gain (<3 dB). In this work, two relatively compact and efficient planar reconfigurable antennas, has been designed and fabricated. The proposed antennas work in either single or dual frequency modes with an adequate gain, depending on the status of the lumped-element switch installed in the radiating patch. The subsequent sections of the paper are organized as follows: Section 2 explains the geometry and design theory of the proposed, i.e. Nine and Epsilon shaped antennas. Measured and simulated results are compared and discussed in section 3. The paper is concluded in section 4. 2. Design and Relevant Theory This part presents theory and design procedure of the proposed antennas. Fig. 1 present the layout of the proposed ‘nine’ and ‘epsilon’ shaped reconfigurable antennas. The radiating element is printed on a low cost and easily available FR-4 substrate, having a relative permittivity and loss tangent of 4.3 and 0.02, respectively. The substrate is backed by a truncated metallic ground plane to obtain better efficiency, gain and bandwidth. The designed antennas are excited
using a 3 mm wider microstrip line with a characteristic impedance of 50 ohms. In order to excite the antennas; a waveguide port is assigned to the microstrip line. A slot of 1 mm width is reserved in the radiating element of the antenna to incorporate the switch (SW) at the right position. The net dimension of the proposed antennas are 35×53×1.6 mm3. The effective resonant length of the antennas for a specific resonant frequency (fr) is calculated using the well-known transmission line theory [21]: (1)
Where, c is the speed of light equal to 3×108 ms-1 , εr is relative permittivity of the substrate and h is the thickness of the substrate. The various dimensions of the
Ant1
antennas are listed in Table 1.
Y
Z X
Ant2
SW
Front view
Rear view
Figure 1: Various geometrical views of the proposed antennas Table 1: Dimensions of the proposed antennas Length
D1 D2 D3 D4 D5 Df Ds Dw W
Ant1 Value (mm) 7
3
5
4
6
18 40
Length
L2
Ls
Lg
r1
r2
2.5 40
13
8
10 20
L1
35
S1 S2
3 W2
Ant2 Value (mm) 17
12
5.9
3. Results In this section the performance matrices (gain, reflection coefficient, and surface currents) of the two antennas are discussed. The simulations are performed using the CST MWS (2015). The antennas were fabricated using a cheaper FR-4 substrate (Fig. 2). The measurements are performed using a Vector Network Analyzer (VNA) and anechoic chamber at National University of
Science and Technology (NUST) Islamabad. The antennas works in a dualband and single band modes when the switch (SW) is turned ON and OFF respectively (Table 2). For the proof of concept the switch is turned ON by using a shorting wire across the gap reserved for the switch. It is turned OFF when the gap is left open. By altering the state of the switch the proposed antenna operates in single band (3.50 GHz) and dual band (2.45 and 5.20 GHz) modes. Table 2: Switching modes for Ant1 and Ant2 Switch status
Frequency band (GHz)
1. Dualband
ON
2.45 and 5.20
2. Single band
OFF
3.50
Ant2
Ant1
Mode
Front view
Rear View
Figure 2: Different views of the fabricated antennas 3.1. Reflection coefficient (S11) The two antennas operates in a frequency mode 1, when switch (SW) is turned ON. In this frequency mode it give resonance at the lower (2.45 GHz) and upper (5.2 GHz) bands (Fig. 3a). When the switch (SW) is in off condition, the antennas work in the single-band mode at 3.5 GHz (Fig. 3b).
(a)
(b)
Figure 3: Simulated and measured reflection coefficient of the proposed antennas (a) Switch ON (b) Switch OFF Both antennas give a significant amount of driving point impedance bandwidth (S11<-10 dB) in all the three frequency bands. I.e. a bandwidth of (13.5%, 35.72% and 9.94%) and (14.46 %, 27.07 %. and 6.15 %) at 2.45, 3.50 and 5.20 GHz, is attained by the Ant1 and Ant2, respectively. 3.2. Radiation patterns and current distribution The simulated and measured gain patterns of the proposed antennas in the Eplane (YZ, ϕ=900) and H-plane (XZ, ϕ=00) at 2.45, 3.5 and 5.2 GHz are portrayed in Fig. 4. The radiation patterns of the two antennas have been measured in the anechoic chamber (Fig. 5). The Ant1 gives a peak gain of 1.7 dB at 2.45 GHz, 2.5 dB at 3.5 GHz and 3.4 dB at 5.2 GHz. Ant2 gives a maximum gain of 1.92 dB, 2.57 dB and 3.01 dB at 2.45, 3.5 and 5.2 GHz, respectively. The antenna radiates omni-directionally in the H-plane for all the three frequency bands. A ‘Figure of eight’ shape radiation pattern is achieved in the E-plane at 2.45 and 3.5 GHz with a null located at θ= 900. At 5.2 GHz the location of null lobe for Ant1 has been shifted to θ= 600 in the E-plane. The measured and simulated gain patterns were found to be in reasonable agreement both principal planes. Both antennas function efficiently with a radiation efficiency>85 % in the desired frequency bands.
2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 4: Simulated and measured gain patterns in both principal planes The distribution of the surface currents of the proposed antennas at 2.45, 3.50 and 5.20 GHz are illustrated in Fig. 6. The segments of the radiating element where the surface current density is maximum and which primarily contributes in generating a given frequency band are encircled in the figure. In Ant1, the loop in the 9-shape and vertical segment below the switch position shows maximum current density to generate the 2.45 GHz band. The current density is prominent below the switch position in Ant1 to give resonance at 3.5 GHz. The loop of the 9-shape radiating element is disconnected in this off-switch frequency mode.
Probe (Horn Antenna) Antenna Under Test (Ant2)
Positioner
Probe (Horn Antenna)
Antenna Under Test (Ant1)
Positioner
Figure 5: Measurement setup of Ant1 and Ant2 in anechoic chamber
The current distribution is maximum across the loop segment of Ant1 to generate the upper frequency band (5.2 GHz). In Ant2 the entire epsilon segment and some part of the feedline shows maximum current density to generate the lower frequency band of 2.45 GHz. The lower part of the epsilon shape segment shows higher current density below the switch position to give resonance at 3.5 GHz. The upper part of the epsilon segment is disconnected in this off-state switching mode and hence does not contribute in generating this frequency mode. To generate the upper frequency band of 5.2 GHz, the epsilon-shape segment of Ant2 is excited for maximum current density. 2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 6: Surface current plots of the proposed antennas at different frequency bands
4. Conclusion In this paper two antennas of reasonable size, have been designed, fabricated, measured and validated. The proposed antennas works in different frequency modes, depending on the switch position. I.e. the antennas operates in dual frequency mode when the switch is turned ON. In contrast, when the switching state is in OFF mode, the designed antennas works in single frequency mode. The simulated results are found in close agreement with the measured results. Both the monopole antennas give an acceptable gain (1.7-3.4 dB), efficiency (85-90%) and bandwidth (6-35%), in the desired frequency bands for a given switching state. The monopoles have an omni-directional pattern in the H-plane. The antennas have an affordable size which enable them to be easily integrated in portable devices such as laptops, tablets and mobile phones.
Acknowledgements The authors of the manuscript thankfully acknowledge, National University of Sciences and Technology (NUST), Islamabad, Pakistan for its support in the required measurements at Research Institute for Microwave and Millimeter-wave Studies (RIMMS). We wish to thank Dr. James Flint of Loughborough University, United Kingdom, for his useful suggestions in modelling of the proposed antennas. We are especially thankful to BOASAR, UET Peshawar for funding this research.
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Sadiq Ullah is Assistant Professor and Head of Telecommunication Engineering Department, University of Engineering & Technology, Peshawar, Pakistan. Sadiq Ullah received B.Sc. Electrical Engineering from University of Engineering and Technology, Peshawar, Pakistan. He achieved his M.Sc. in Electrical Engineering from University of Engineering and Technology Taxila, Pakistan. In 2007, he joined the Department of Electronic and Electrical Engineering, at Loughborough University, U.K., and was awarded Ph.D. for his research in the field of design and measurement of metamaterial based antennas in 2010. He worked as an Assistant Manager (Electronics) in a public sector R and D organization in Islamabad, where his main responsibilities were hardware, software co-design, designing and testing of high precession electronics, test equipment. His research mainly focuses on design and measurement of low-profile antennas on electromagnetic Bandgap structures, RFID tag antennas and wearable antennas. He has been worked as a Research Associate at Loughborough University, where he researched on the propagation effects of rain, snow, ice, fog and forest in millimeter wave band. During his Ph.D., he published his research in international conferences and journals. ORCID: http://orcid.org/0000-0002-5299-1577 E-mail: [email protected] Shahzeb Hayat is a research student in the Department of Biomedical Engineering, Ulsan University, South Korea. His research interests include planar antenna, millimeter wave antennas, multi band antennas, implanted antennas, Specific Absorption Rate analysis, Frequency Selective Surfaces and EBGs.
Anees Umar is a research student in UET Peshawar, Pakistan in the Department of Telecommunication Engineering, UET Peshawar (Mardan Campus), Pakistan. Currently he is doing research on reconfigurable antennas. His research interests include, planar antennas, millimeter wave antennas and metamaterial surfaces. Usman Ali received his B.Sc. Telecommunication Engineering from University of Engineering and Technology, Peshawar, Pakistan in 2012. He received his M.Sc. in Telecommunication Engineering from University of Engineering and Technology Peshawar, Pakistan in 2017. His research interests include metamaterials, signal processing, Electromagnetic Bandgap structures and wearable antennas. Currently he is working as a Lab Engineer in the same Department. Farooq Ahmad Tahir was born in Faisalabad, Pakistan. He received BE degree in Electrical Engineering from University of Engineering and Technology Lahore, Pakistan in 2005. In 2008, He was awarded Master’s Degree in Radio Frequency Telecommunications and Microelectronics (TRFM) from the University of Nice, Sophia Antipolis, France. During his PhD, his research was focused on “Electromagnetic Modeling, Design and Implementation of Printed Electronically Reconfigurable Reflect array Antenna Systems for LEO Satellites”. This Research was carried out under European Space Agency (ESA), Thales Alenia Space, and French Research Agency. He received Doctorate degree in September 2011 from National Polytechnique Institute of Toulouse (INPT), University of Toulouse, France. His PhD thesis was nominated for Best Thesis Prize for the year 2011 at National Polytechnique Institute of Toulouse, France. Currently he is Assistant Professor in Research Institute for Microwave and Millimeter-wave Studies (RIMMS), National University of Sciences and Technology (NUST), Islamabad, Pakistan James Flint is Reader in Wireless Systems Engineering, Head of the Communications Research Division within the School of Mechanical, Electrical and Manufacturing Engineering. His research focuses on various aspects of wireless systems, especially in the area of transducer design in electromagnetic and acoustics. He has a keen interest in biomimetics, ultrasound and on
converting systems found in nature into workable engineering solutions. Dr Flint was previously employed in the automotive industry and maintains an interest in safety-critical systems, installed performance of antennas and electromagnetic compatibility. In recent years Dr Flint has had a particular interest in band gap structures (both electromagnetic and acoustic).
Figure Captions: Figure 2: Various geometrical views of the proposed antennas Figure 2: Different views of the fabricated antennas Figure 3: Simulated and measured reflection coefficient of the proposed antennas (a) Switch ON (b) Switch OFF Figure 4: Simulated and measured gain patterns in both principal planes Figure 5: Measurement setup of Ant1 and Ant2 in anechoic chamber Figure 6: Surface current plots of the proposed antennas at different frequency bands
Ant1 Y
Z X
Ant2
SW
Front view
Rear view
Figure 3: Various geometrical views of the proposed antennas
Ant1 Ant2
Front view
Rear View
Figure 2: Different views of the fabricated antennas
(a)
(b) Figure 3: Simulated and measured reflection coefficient of the proposed antennas (a) Switch ON (b) Switch OFF
2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 4: Simulated and measured gain patterns in both principal planes
Probe (Horn Antenna) Antenna Under Test (Ant2)
Positioner
Probe (Horn Antenna)
Antenna Under Test (Ant1)
Positioner
Figure 5: Measurement setup of Ant1 and Ant2 in anechoic chamber
2.45 GHz
3.50 GHz
5.20 GHz
Ant2
Ant1
fr
Figure 6: Surface current plots of the proposed antennas at different frequency bands