- Email: [email protected]
Miniaturization of patch antennas by curved edges
Journal Pre-proofs Regular paper Miniaturization of Patch Antennas by Curved Edges Ali Farahbakhsh, Davoud Zarifi PII: DOI: Reference:
S1434-8411(19)32669-X https://doi.org/10.1016/j.aeue.2020.153125 AEUE 153125
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
23 October 2019 9 February 2020
Please cite this article as: A. Farahbakhsh, D. Zarifi, Miniaturization of Patch Antennas by Curved Edges, International Journal of Electronics and Communications (2020), doi: https://doi.org/10.1016/j.aeue. 2020.153125
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.
© 2020 Published by Elsevier GmbH.
Miniaturization of Patch Antennas by Curved Edges Ali Farahbakhsh1 and Davoud Zarifi2
Abstract Due to the development of mobile communication devices, the miniaturized antenna design is becoming an important consideration today. In this paper, a new small microstrip antenna is proposed in which the patch is curved along its width to force the electrical currents to move in a longer path. Consequently, the electrical size of patch is increased so that its physical size is decreased to almost 63.5% of the size of common rectangular patch antenna. Furthermore, the measurement results show that the return loss of the proposed antenna is enhanced compared to the rectangular patch antenna while their radiation patterns are the same. Keywords: Compact Size, Curved Patch, Microstrip Patch Antenna, Miniaturization. 1- Introduction The microstrip antennas are very popular because of their small size, low cost, light weight, simple fabrication and flexibility [1-3]. As the mobile devices are developed further, small antennas attract great attention. Therefore, many techniques have been proposed to decrease the size of microstrip antennas [4-14]. The simplest method is to utilize high permittivity substrate to decrease the patch size which increases the product costs and deteriorates the antenna efficiency due to the dielectric loss [4]. Metamaterials as left handed materials are used to reduce the patch size [5-7]. However, this method increases the structure complexity and leads to expensive antennas. Some methods are proposed for size reduction by using fractal shapes as radiating patch [8, 9]. But in most cases, the radiation patterns are changed greatly due to the asymmetry patch shape. Meanwhile, some papers are presented to decrease patch size by applying reactive/resistive loads to antenna patch which leads to antenna losses increment [10, 11].
Department of Electrical and Computer Engineering, Graduate University of Advanced Technology, Kerman, Iran. Email: [email protected] 2 School of Electrical Engineering, University of Kashan, Kashan, Iran Email: [email protected] 1
1
In this paper, a new patch configuration using curved edges is proposed to reduce the size of microstrip antennas, so that the currents on the patch are forced to travel longer paths [15, 16]. Consequently, the electrical size of the patch will be increased. Its advantage is that the pattern and polarization of the modified antenna are identical to those of the rectangular patch. This method can be combined with other techniques to obtain better results. First, the antenna patch edges are made curved and its effect on antenna resonant frequency and electrical size are investigated. Then, an optimal small antenna is obtained by implementing Genetic Algorithm optimization. Finally, the optimal antenna is manufactured and the measurement results are compared to the simulated ones. The proposed method can be combined with the other size reduction techniques such as using meta-material substrate to achieve more compact antenna. The concept and applicability of the proposed method is shown and proved using simulation and measurement results. 2- Antenna Structure The antenna considered here is a rectangular patch microstrip antenna and is fed by the proximity feeding method. Its layered structure includes three conductive planes and two dielectric substrates as shown in Fig. 1. The patch is placed on the top plane, the middle plane is the feed structure and the lower plane acts as an infinite ground plane. ROGERS RO4003 is utilized as substrate which its relative permittivity ( r ) is 3.38 and its dissipation factor (tanδ) is 0.0027 at 10 GHz. The thickness of substrates (D1, D2) is 0.508 mm. The antenna is designed for the X band at 10 GHz. So its width and length are calculated to be 10 mm and 7.52 mm, respectively, as shown in Fig. 2(a). The patch is fed by a 50 ohm line. The edges of patch are curved along its width. The curved edge is circular with depth h. Fig. 2(b) illustrates a typical patch antenna with two curved edges.
Figure 1. Layered structure of the antenna
2
(a)
(b)
Figure 2. Regular rectangular (a) and concave rectangular (b) patch antennas
Resonant Frequency / F0
1 0.99 0.98 0.97 0.96 0.95 0.94 0.93
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14 0.15
h/L
Figure 3. Antenna resonant frequency versus patch concavity.
(a)
(b)
Figure 4. Electric Current in (a) regular patch antenna and (b) concave patch antenna.
3
3- Patch Concavity Effect In this section the effect of patch with curved edge on resonant frequency of antenna is investigated. The ground plane of the antennas is considered to be infinite ground in the simulation to speed up the simulation. By introducing curvature in the patch edge, the electric currents are forced to travel longer path that leads to increment in patch electrical length. By using some geometric relationships, the electrical path increment can be formulated as following by considering small value of h compare to the patch length (L). 𝐿2
ℎ 4
1 ℎ 2
∆𝐿 = ℎ 𝑠𝑖𝑛 ―1( (𝐿) + 2(𝐿) )
(1)
According to Eq. (1), it is obvious that by increasing h, the currents are compelled to travel longer path and consequently, the resonant frequency of the patch is reduced. To show the effect of curvature, the resonant frequency of the curved edge patch is simulated. The simulation is performed by FEKO software [17] which is based on Method of Moments (MOM). Fig 3 illustrates the effect of curved edge patch on antenna resonant frequency. The regular rectangular patch is shown by h = 0. Observe in Fig. 3 that the antenna resonant frequency is shifted down by increasing h. In other words, the electrical size of patch is increased by increasing the value of h. As shown in Fig. 4, in the patch with curved edges, the currents travel longer paths than in the regular patch. Therefore, the electrical length of curved-edge-patch is longer than the regular patch and its resonant frequency is lower. To compensate this effect, the patch physical size should be decreased that leads to size reduction of the patch antenna. The xcomponents of curved-patch currents neutralize the effect of each other in the far-field due to their opposite polarity. So the far-field radiation pattern and polarization of the curved-edge patch does not differ from the rectangular patch. 4- Optimization Process It is difficult to calculate patch dimensions and circular curvature depth (h) for a desired resonant frequency by trial and error. Therefore, an optimization method is used in here to obtain a small antenna with the acceptable return loss. The enhanced genetic algorithm [18] is employed to optimize the patch antenna. The enhanced genetic algorithm is proposed to improve the speed and accuracy of the classical GA. The main idea of this method is to utilize a fuzzy system to control the crossover and mutation rates based on the algorithm convergence rate during its process running which is describe deeply in [18]. The patch width, length and circular depth are optimized to obtain an antenna with the least amount of return loss and the smallest size. The optimization program is written in MATLAB [19] and linked to FEKO for electromagnetic simulations. The following results are obtained for optimal concave antenna W = 8.14 mm, L = 7.03 mm and h = 1.005 mm while the dimensions of the reference rectangular patch antenna are W = 10 mm, L = 7.52 mm.
4
Figure 5. Rectangular and concave patches at 10 GHz. The optimal patch antenna and the ordinary rectangular patch antenna are compared and illustrated in Fig. 5. The area of optimal patch is 47.77 mm2 and the area of ordinary rectangular patch is 75.2 mm2, so the size of proposed antenna is 36.5% smaller than rectangular patch.
Reflection Coefficient (dB)
0 -5 -10 -15 Rectangular Patch Concave Patch
-20 -25 -30 -35 -40 9.5
9.6
9.7
9.8
9.9
10
10.1
10.2
10.3
10.4
10.5
Frequency (GHz)
Figure 6. Simulated reflection coefficients of rectangular and concave patch antenna.
5
Figure 7. Input impedance of the proposed antenna (dashed line) and rectangular antenna (solid line) on the smith chart versus frequency The reflection coefficients of rectangular and curved-edge patch antenna are shown in Fig. 6. Observe that an excellent input impedance matching is achieved at the center frequency and the reflection coefficient of both structures are below -25 dB. The impedance bandwidth of the rectangular patch and concave patch are 4 % and 3%, respectively. In addition, the input impedances of both structures are plotted on Smith Chart versus frequency which is shown in Fig. 7. As can be seen, very good matching is obtained at center frequency. Fig. 8 shows the radiation patterns of curved-edge and straight-edge rectangular patch antennas. Observe that the radiation pattern of both antennas are very similar, but the gain of curved-edge antenna at θ = φ = 0° is about 5.2 dB, which is 0.45 dB less than that of the straight-edge rectangular patch antenna at this point. Its reason is that the physical size of the proposed antenna is smaller than the rectangular patch size. In addition, the total efficiency of the proposed antenna, which includes ohmic, mismatch and aperture losses, is about 82 % which is lower than the total efficiency of the rectangular patch antenna (90 %) due to size reduction. However, the difference is not significant and the radiation properties of the proposed antenna is acceptable. The axial ratio of the proposed antenna is 49.8 dB at θ = φ = 0° showing that the proposed antenna has a good linear polarization.
6
(a)
(b) Figure 8. Realized gain radiation pattern of (a) concave and (b) rectangular patch antenna at center frequency (10 GHz) the units are dBi versus degree. 5- Manufactured Structures To validate the design and show its applicability, the optimum curved-edge patch antenna is fabricated as well as the ordinary rectangular patch antenna that are shown in Fig. 9. The measured reflection coefficients of both antennas are plotted in Fig. 10. As can be seen, the measured results are in good agreement with the simulated ones, except a few shift in the center frequencies which is due to the fabrication tolerances which is negligible.
7
(a)
(b)
(c) Figure 9. (a) Layers of the antennas and top and bottom view of the fabricated (b) rectangular patch antenna and (c) concave patch antenna.
8
Reclection Ceofficient (dB)
0
-10 Concave Patch Meas. Rec. Patch Meas. Concave Patch Sim. Rec. Patch Sim.
-20
-30
-40
9
9.2
9.4
9.6
9.8
10
10.2
10.4
10.6
10.8
11
Frequency (GHz)
Figure 10. Measured and simulation reflection coefficient of the rectangular and concave patch antennas.
Fig. 11 shows the measured normalized radiation patterns. Some back-lobs are appeared compare to the simulation results. This difference is due to the finite ground plans that are used for fabrication while in the simulation infinite grounds are utilized. However, the more important issue is that the radiation patterns of the proposed antenna are similar to the rectangular ones which means the concavity does not disturb the radiation property of the antenna.
E-Plane data1
30
H-Plane data2
0
330 330 00
60
-5 -10 -15 -20
90
300 300
270 270
120 120
240 240 150 150
180 180
(a)
9
210 210
E-Plane
30
H-Plane
0
330 0
60
-5 -10 -15 -20
90
300
270
120
240 150
180
210
(b) Figure 11. Measured normalized radiation patterns of (a) concave patch antenna and (b) rectangular patch antenna at the center frequency, units are dBi versus degree.
6- Conclusion A new method of miniaturization of the rectangular patch antenna has been presented in this paper. The patch edge is made circular along its width, so that the electrical currents pass along longer paths and the electrical size of the patch is increased. The proposed method can be combined with the other size reduction methods to obtain more compact antenna. The optimally miniaturized patch antenna is obtained by using the genetic algorithm. The simulation results show that this method is suitable to design small patch antenna. The proposed antenna is fabricated and its measured results are compared to the results of the rectangular patch antenna to validate the design procedure. The proposed design procedure can be applied at desirable frequency range for desirable application such as terrestrial communications and networking, point to point links, military and amateur radio. ACKNOLEGMENT The authors would like to acknowledge from Ali Nazari Ouderji, technical expert in Intelligent Boards Electronic Company, for his valuable efforts for fabrication process of the antenna. REFERENCES [1] Constantine A. Balanis, “Antenna Theory: Analysis and Design”, third ed., Wiley, 2005.
10
[2] C. A. Balanis, “Modern Antenna Handbook”, JohnWiley & Sons,New York, NY, USA, 2008. [3] J. L. Volakis, “Antenna Engineering Handbook”, fourth ed., Digital Engineering Library @ McGraw-Hill, 2007. [4] Lo, T. K. and Y. Hwang, “Microstrip antennas of very high permittivity for personal communications,” 1997 Asia Pacific Microwave Conference, 253–256, 1997. [5] F. Bilotti, A. Alù, N. Engheta and L. Vegni, "Miniaturized Circular Patch Antenna with Metamaterial Loading", The European Conference on Anten-nas and Propagation, France, 2006. [6] A. A. Fashi, M. Kamyab, and M. Barati, "A Microstrip Small-Sized Array Antenna Based on the Meta-Material Zeroth-Order Resonator", Progress In Electromagnetics Research C, Vol. 14, pp. 89-101, 2010. [7] Gohar Varamini, Asghar Keshtkar, Mohammad Naser-Moghadasi, “Compact and miniaturized microstrip antenna based on fractal and metamaterial loads with reconfigurable qualification”, AEU International Journal of Electronics and Communications,Volume 83, 2018. [8] Z.-W. Yu, G.-M. Wang, X.-J. Gao, and K. Lu, “A Novel Small-Size Single Patch Microstrip Antenna Based on Koch and Sierpinski FractalShapes”, Progress In Electromagnetics Research Letters, Vol. 17, pp. 95103, 2010. [9] A. Kordzadeh and F. Hojat Kashani, “A New Reduced Size Microstrip Patch Antenna with Fractal Shaped Defects”, Progress In Electromagnetics Research B, Vol. 11, pp. 29–37, 2009. [10] M.C. Liang, Y.M. Chen, C.C. Huang and W.S. Chen, "An electrically small impedance-matched microstrip antenna design ", Antennas and Propaga-tion Society International Symposium, Vol. 4, pp. 38-41, 2002. [11] P. Ferrari, N. Corrao and D. Rauly, "Miniaturized circular patch antenna with capacitors loading", Microwave and Optoelectronics Conference, 2007. [12] Hongyu Shi, Jianxing Li, Junwei Shi, Juan Chen, Zhiyuan Li, Shitao Zhu, Tayyab Ali Khan, Anxue Zhang, “Miniaturized circularly polarized patch antenna using coupled shorting strip and capacitive probe feed”, AEU - International Journal of Electronics and Communications, Volume 98, 2019. [13] Falguni Raval, Y.P. Kosta, Harshita Joshi, “Reduced size patch antenna using complementary split ring resonator as defected ground plane”, AEU - International Journal of Electronics and Communications, Volume 69, Issue 8, 2015. [14] Shahrokh Jam, Mojtaba Simruni, “Performance enhancement of a compact wideband patch antenna array using EBG structures”, AEU International Journal of Electronics and Communications,Volume 89,2018.
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[15] S. Mohanna, A. Farahbakhsh, S. Tavakoli, and N. Ghassemi, “Reduction ofMutual Coupling and Return Loss in Microstrip Array Antennas Using Concave Rectangular Patches”, International Journal of Microwave Science and Technology, Vol. 2010, Dec 2010. [16] A. Farahbakhsh, S. Mohanna, S. Tavakoli and M. O. Sadegh, "New patch configurations to reduce the mutual coupling in microstrip array antenna," 2009 Loughborough Antennas & Propagation Conference, Loughborough, 2009, pp. 469-472. [17] FEKO 6.0, Copyright 2005-2012, EM Software & Systems-S.A. (Pty) Ltd. [18] A. Farahbakhsh, S. Tavakoli and A. Seifolhosseini, "Enhancement of Genetic Algorithm and Ant Colony Optimization Techniques using Fuzzy Systems," 2009 IEEE International Advance Computing Conference, India, 2009, pp. 336-339. [19] Matlab the language of technical computing, The mathworks Inc.
12
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
13
S1434-8411(19)32669-X https://doi.org/10.1016/j.aeue.2020.153125 AEUE 153125
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
23 October 2019 9 February 2020
Please cite this article as: A. Farahbakhsh, D. Zarifi, Miniaturization of Patch Antennas by Curved Edges, International Journal of Electronics and Communications (2020), doi: https://doi.org/10.1016/j.aeue. 2020.153125
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.
© 2020 Published by Elsevier GmbH.
Miniaturization of Patch Antennas by Curved Edges Ali Farahbakhsh1 and Davoud Zarifi2
Abstract Due to the development of mobile communication devices, the miniaturized antenna design is becoming an important consideration today. In this paper, a new small microstrip antenna is proposed in which the patch is curved along its width to force the electrical currents to move in a longer path. Consequently, the electrical size of patch is increased so that its physical size is decreased to almost 63.5% of the size of common rectangular patch antenna. Furthermore, the measurement results show that the return loss of the proposed antenna is enhanced compared to the rectangular patch antenna while their radiation patterns are the same. Keywords: Compact Size, Curved Patch, Microstrip Patch Antenna, Miniaturization. 1- Introduction The microstrip antennas are very popular because of their small size, low cost, light weight, simple fabrication and flexibility [1-3]. As the mobile devices are developed further, small antennas attract great attention. Therefore, many techniques have been proposed to decrease the size of microstrip antennas [4-14]. The simplest method is to utilize high permittivity substrate to decrease the patch size which increases the product costs and deteriorates the antenna efficiency due to the dielectric loss [4]. Metamaterials as left handed materials are used to reduce the patch size [5-7]. However, this method increases the structure complexity and leads to expensive antennas. Some methods are proposed for size reduction by using fractal shapes as radiating patch [8, 9]. But in most cases, the radiation patterns are changed greatly due to the asymmetry patch shape. Meanwhile, some papers are presented to decrease patch size by applying reactive/resistive loads to antenna patch which leads to antenna losses increment [10, 11].
Department of Electrical and Computer Engineering, Graduate University of Advanced Technology, Kerman, Iran. Email: [email protected] 2 School of Electrical Engineering, University of Kashan, Kashan, Iran Email: [email protected] 1
1
In this paper, a new patch configuration using curved edges is proposed to reduce the size of microstrip antennas, so that the currents on the patch are forced to travel longer paths [15, 16]. Consequently, the electrical size of the patch will be increased. Its advantage is that the pattern and polarization of the modified antenna are identical to those of the rectangular patch. This method can be combined with other techniques to obtain better results. First, the antenna patch edges are made curved and its effect on antenna resonant frequency and electrical size are investigated. Then, an optimal small antenna is obtained by implementing Genetic Algorithm optimization. Finally, the optimal antenna is manufactured and the measurement results are compared to the simulated ones. The proposed method can be combined with the other size reduction techniques such as using meta-material substrate to achieve more compact antenna. The concept and applicability of the proposed method is shown and proved using simulation and measurement results. 2- Antenna Structure The antenna considered here is a rectangular patch microstrip antenna and is fed by the proximity feeding method. Its layered structure includes three conductive planes and two dielectric substrates as shown in Fig. 1. The patch is placed on the top plane, the middle plane is the feed structure and the lower plane acts as an infinite ground plane. ROGERS RO4003 is utilized as substrate which its relative permittivity ( r ) is 3.38 and its dissipation factor (tanδ) is 0.0027 at 10 GHz. The thickness of substrates (D1, D2) is 0.508 mm. The antenna is designed for the X band at 10 GHz. So its width and length are calculated to be 10 mm and 7.52 mm, respectively, as shown in Fig. 2(a). The patch is fed by a 50 ohm line. The edges of patch are curved along its width. The curved edge is circular with depth h. Fig. 2(b) illustrates a typical patch antenna with two curved edges.
Figure 1. Layered structure of the antenna
2
(a)
(b)
Figure 2. Regular rectangular (a) and concave rectangular (b) patch antennas
Resonant Frequency / F0
1 0.99 0.98 0.97 0.96 0.95 0.94 0.93
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14 0.15
h/L
Figure 3. Antenna resonant frequency versus patch concavity.
(a)
(b)
Figure 4. Electric Current in (a) regular patch antenna and (b) concave patch antenna.
3
3- Patch Concavity Effect In this section the effect of patch with curved edge on resonant frequency of antenna is investigated. The ground plane of the antennas is considered to be infinite ground in the simulation to speed up the simulation. By introducing curvature in the patch edge, the electric currents are forced to travel longer path that leads to increment in patch electrical length. By using some geometric relationships, the electrical path increment can be formulated as following by considering small value of h compare to the patch length (L). 𝐿2
ℎ 4
1 ℎ 2
∆𝐿 = ℎ 𝑠𝑖𝑛 ―1( (𝐿) + 2(𝐿) )
(1)
According to Eq. (1), it is obvious that by increasing h, the currents are compelled to travel longer path and consequently, the resonant frequency of the patch is reduced. To show the effect of curvature, the resonant frequency of the curved edge patch is simulated. The simulation is performed by FEKO software [17] which is based on Method of Moments (MOM). Fig 3 illustrates the effect of curved edge patch on antenna resonant frequency. The regular rectangular patch is shown by h = 0. Observe in Fig. 3 that the antenna resonant frequency is shifted down by increasing h. In other words, the electrical size of patch is increased by increasing the value of h. As shown in Fig. 4, in the patch with curved edges, the currents travel longer paths than in the regular patch. Therefore, the electrical length of curved-edge-patch is longer than the regular patch and its resonant frequency is lower. To compensate this effect, the patch physical size should be decreased that leads to size reduction of the patch antenna. The xcomponents of curved-patch currents neutralize the effect of each other in the far-field due to their opposite polarity. So the far-field radiation pattern and polarization of the curved-edge patch does not differ from the rectangular patch. 4- Optimization Process It is difficult to calculate patch dimensions and circular curvature depth (h) for a desired resonant frequency by trial and error. Therefore, an optimization method is used in here to obtain a small antenna with the acceptable return loss. The enhanced genetic algorithm [18] is employed to optimize the patch antenna. The enhanced genetic algorithm is proposed to improve the speed and accuracy of the classical GA. The main idea of this method is to utilize a fuzzy system to control the crossover and mutation rates based on the algorithm convergence rate during its process running which is describe deeply in [18]. The patch width, length and circular depth are optimized to obtain an antenna with the least amount of return loss and the smallest size. The optimization program is written in MATLAB [19] and linked to FEKO for electromagnetic simulations. The following results are obtained for optimal concave antenna W = 8.14 mm, L = 7.03 mm and h = 1.005 mm while the dimensions of the reference rectangular patch antenna are W = 10 mm, L = 7.52 mm.
4
Figure 5. Rectangular and concave patches at 10 GHz. The optimal patch antenna and the ordinary rectangular patch antenna are compared and illustrated in Fig. 5. The area of optimal patch is 47.77 mm2 and the area of ordinary rectangular patch is 75.2 mm2, so the size of proposed antenna is 36.5% smaller than rectangular patch.
Reflection Coefficient (dB)
0 -5 -10 -15 Rectangular Patch Concave Patch
-20 -25 -30 -35 -40 9.5
9.6
9.7
9.8
9.9
10
10.1
10.2
10.3
10.4
10.5
Frequency (GHz)
Figure 6. Simulated reflection coefficients of rectangular and concave patch antenna.
5
Figure 7. Input impedance of the proposed antenna (dashed line) and rectangular antenna (solid line) on the smith chart versus frequency The reflection coefficients of rectangular and curved-edge patch antenna are shown in Fig. 6. Observe that an excellent input impedance matching is achieved at the center frequency and the reflection coefficient of both structures are below -25 dB. The impedance bandwidth of the rectangular patch and concave patch are 4 % and 3%, respectively. In addition, the input impedances of both structures are plotted on Smith Chart versus frequency which is shown in Fig. 7. As can be seen, very good matching is obtained at center frequency. Fig. 8 shows the radiation patterns of curved-edge and straight-edge rectangular patch antennas. Observe that the radiation pattern of both antennas are very similar, but the gain of curved-edge antenna at θ = φ = 0° is about 5.2 dB, which is 0.45 dB less than that of the straight-edge rectangular patch antenna at this point. Its reason is that the physical size of the proposed antenna is smaller than the rectangular patch size. In addition, the total efficiency of the proposed antenna, which includes ohmic, mismatch and aperture losses, is about 82 % which is lower than the total efficiency of the rectangular patch antenna (90 %) due to size reduction. However, the difference is not significant and the radiation properties of the proposed antenna is acceptable. The axial ratio of the proposed antenna is 49.8 dB at θ = φ = 0° showing that the proposed antenna has a good linear polarization.
6
(a)
(b) Figure 8. Realized gain radiation pattern of (a) concave and (b) rectangular patch antenna at center frequency (10 GHz) the units are dBi versus degree. 5- Manufactured Structures To validate the design and show its applicability, the optimum curved-edge patch antenna is fabricated as well as the ordinary rectangular patch antenna that are shown in Fig. 9. The measured reflection coefficients of both antennas are plotted in Fig. 10. As can be seen, the measured results are in good agreement with the simulated ones, except a few shift in the center frequencies which is due to the fabrication tolerances which is negligible.
7
(a)
(b)
(c) Figure 9. (a) Layers of the antennas and top and bottom view of the fabricated (b) rectangular patch antenna and (c) concave patch antenna.
8
Reclection Ceofficient (dB)
0
-10 Concave Patch Meas. Rec. Patch Meas. Concave Patch Sim. Rec. Patch Sim.
-20
-30
-40
9
9.2
9.4
9.6
9.8
10
10.2
10.4
10.6
10.8
11
Frequency (GHz)
Figure 10. Measured and simulation reflection coefficient of the rectangular and concave patch antennas.
Fig. 11 shows the measured normalized radiation patterns. Some back-lobs are appeared compare to the simulation results. This difference is due to the finite ground plans that are used for fabrication while in the simulation infinite grounds are utilized. However, the more important issue is that the radiation patterns of the proposed antenna are similar to the rectangular ones which means the concavity does not disturb the radiation property of the antenna.
E-Plane data1
30
H-Plane data2
0
330 330 00
60
-5 -10 -15 -20
90
300 300
270 270
120 120
240 240 150 150
180 180
(a)
9
210 210
E-Plane
30
H-Plane
0
330 0
60
-5 -10 -15 -20
90
300
270
120
240 150
180
210
(b) Figure 11. Measured normalized radiation patterns of (a) concave patch antenna and (b) rectangular patch antenna at the center frequency, units are dBi versus degree.
6- Conclusion A new method of miniaturization of the rectangular patch antenna has been presented in this paper. The patch edge is made circular along its width, so that the electrical currents pass along longer paths and the electrical size of the patch is increased. The proposed method can be combined with the other size reduction methods to obtain more compact antenna. The optimally miniaturized patch antenna is obtained by using the genetic algorithm. The simulation results show that this method is suitable to design small patch antenna. The proposed antenna is fabricated and its measured results are compared to the results of the rectangular patch antenna to validate the design procedure. The proposed design procedure can be applied at desirable frequency range for desirable application such as terrestrial communications and networking, point to point links, military and amateur radio. ACKNOLEGMENT The authors would like to acknowledge from Ali Nazari Ouderji, technical expert in Intelligent Boards Electronic Company, for his valuable efforts for fabrication process of the antenna. REFERENCES [1] Constantine A. Balanis, “Antenna Theory: Analysis and Design”, third ed., Wiley, 2005.
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[2] C. A. Balanis, “Modern Antenna Handbook”, JohnWiley & Sons,New York, NY, USA, 2008. [3] J. L. Volakis, “Antenna Engineering Handbook”, fourth ed., Digital Engineering Library @ McGraw-Hill, 2007. [4] Lo, T. K. and Y. Hwang, “Microstrip antennas of very high permittivity for personal communications,” 1997 Asia Pacific Microwave Conference, 253–256, 1997. [5] F. Bilotti, A. Alù, N. Engheta and L. Vegni, "Miniaturized Circular Patch Antenna with Metamaterial Loading", The European Conference on Anten-nas and Propagation, France, 2006. [6] A. A. Fashi, M. Kamyab, and M. Barati, "A Microstrip Small-Sized Array Antenna Based on the Meta-Material Zeroth-Order Resonator", Progress In Electromagnetics Research C, Vol. 14, pp. 89-101, 2010. [7] Gohar Varamini, Asghar Keshtkar, Mohammad Naser-Moghadasi, “Compact and miniaturized microstrip antenna based on fractal and metamaterial loads with reconfigurable qualification”, AEU International Journal of Electronics and Communications,Volume 83, 2018. [8] Z.-W. Yu, G.-M. Wang, X.-J. Gao, and K. Lu, “A Novel Small-Size Single Patch Microstrip Antenna Based on Koch and Sierpinski FractalShapes”, Progress In Electromagnetics Research Letters, Vol. 17, pp. 95103, 2010. [9] A. Kordzadeh and F. Hojat Kashani, “A New Reduced Size Microstrip Patch Antenna with Fractal Shaped Defects”, Progress In Electromagnetics Research B, Vol. 11, pp. 29–37, 2009. [10] M.C. Liang, Y.M. Chen, C.C. Huang and W.S. Chen, "An electrically small impedance-matched microstrip antenna design ", Antennas and Propaga-tion Society International Symposium, Vol. 4, pp. 38-41, 2002. [11] P. Ferrari, N. Corrao and D. Rauly, "Miniaturized circular patch antenna with capacitors loading", Microwave and Optoelectronics Conference, 2007. [12] Hongyu Shi, Jianxing Li, Junwei Shi, Juan Chen, Zhiyuan Li, Shitao Zhu, Tayyab Ali Khan, Anxue Zhang, “Miniaturized circularly polarized patch antenna using coupled shorting strip and capacitive probe feed”, AEU - International Journal of Electronics and Communications, Volume 98, 2019. [13] Falguni Raval, Y.P. Kosta, Harshita Joshi, “Reduced size patch antenna using complementary split ring resonator as defected ground plane”, AEU - International Journal of Electronics and Communications, Volume 69, Issue 8, 2015. [14] Shahrokh Jam, Mojtaba Simruni, “Performance enhancement of a compact wideband patch antenna array using EBG structures”, AEU International Journal of Electronics and Communications,Volume 89,2018.
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[15] S. Mohanna, A. Farahbakhsh, S. Tavakoli, and N. Ghassemi, “Reduction ofMutual Coupling and Return Loss in Microstrip Array Antennas Using Concave Rectangular Patches”, International Journal of Microwave Science and Technology, Vol. 2010, Dec 2010. [16] A. Farahbakhsh, S. Mohanna, S. Tavakoli and M. O. Sadegh, "New patch configurations to reduce the mutual coupling in microstrip array antenna," 2009 Loughborough Antennas & Propagation Conference, Loughborough, 2009, pp. 469-472. [17] FEKO 6.0, Copyright 2005-2012, EM Software & Systems-S.A. (Pty) Ltd. [18] A. Farahbakhsh, S. Tavakoli and A. Seifolhosseini, "Enhancement of Genetic Algorithm and Ant Colony Optimization Techniques using Fuzzy Systems," 2009 IEEE International Advance Computing Conference, India, 2009, pp. 336-339. [19] Matlab the language of technical computing, The mathworks Inc.
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Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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