The improvement of antenna parameters is very important. A 4 x 4 array antenna with improved parameters by using multiple substrate layers and Electromagnetic Band Gap (EBG) structure is proposed in this paper.
Nghiên cứu khoa học công nghệ GAIN AND BANDWIDTH ENHANCEMENT FOR ARRAY ANTENNA BY USING MULTI SUBSTRATE LAYERS AND EBG STRUCTURE Nguyen Ngoc Lan*1, To Thi Thao2 and Vu Van Yem1 Abstract: Today, microstrip technology has been used widely thanks to its advantages such as small size, lightweight, low cost and easy fabrication However, microstrip technology also has many challenges for antenna designers due to its disadvantages, for example: low gain, low efficiency and narrow bandwidth Therefore, the improvement of antenna parameters is very important A x array antenna with improved parameters by using multiple substrate layers and Electromagnetic Band Gap (EBG) structure is proposed in this paper The proposed antenna has some benefits: high gain (more 11.4 dBi) and large percentage of bandwidth (approximately 23% - 2.5 GHz for measurement result) and high efficiency (88%) Besides, the antenna has high directivity and low sidelobe level The antenna is designed at central frequency of 11 GHz The antenna is simulated and fabricated on FR4 substrate with thickness of 1.6 mm, εr = 4.4 and tanδ = 0.02 The simulation results are obtained using CST Microwave Studio software and are compared to measurement ones Keywords: Array antenna, Electromagnetic Band Gap (EBG), Multi substrates, Microstrip antenna INTRODUCTION To meet the increasing demands of customers, the enhancement in service quality for wireless communication is essential Therefore, the improvement of antenna parameters is very important Currently, there are many different methods to improve antenna parameters, for example: Defected Ground Structure (DGS), Metamaterial Reflected Surface, multi substrate layers, Electromagnetic Band Gap (EBG) and so on With flexible characteristics, EBG can prevent or assist the propagation of electromagnetic waves; therefore, it is applied widely, especially in microwave and antenna fields EBG is artificial periodic (or sometimes non-periodic) objects that prevent/assist the propagation of electromagnetic waves in a specified band of frequency for all incident angles and all polarization states [1] In general, EBG structures can be categorized into three groups according to their geometric configuration: three-dimensional volumetric structures, twodimensional planar surfaces, and one-dimensional transmission lines In these structures, the uni-planar (UP) structure is the easiest one to be fabricated In addition, the 2D structure is apply the widest in antenna engineering because some of its advantages: low profile, light weight, and low fabrication cost Therefore, this paper proposes a uni-planar structure for EBG By using EBG structure, some parameters of antenna can be improved such as bandwidth, gain, directivity, efficiency Besides, with some benefits such as high directivity and high gain, array antenna is used in more and more applications such as mobile termination, satellite communication, radar Therefore, using array antenna is also one of the ways to improve parameters There are many published scientific papers about array antenna [2-4] However, there are some limitations in these papers In [2] although the antenna is designed at frequency of 35 GHz, the efficiency of antenna is only 67% With this efficiency, the antenna can not operate well In another study [3], the 8x8 array antenna is designed at E-band (greater than 70 GHz), but the percentage of bandwidth of antenna is only approximately 2.6% and 1.7% In addition, the efficiency of antenna is only from 60% to 70% Similarly, although the x array Tạp chí Nghiên cứu KH&CN quân sự, Số 50, 08 - 2017 11 Kỹ thuật điều khiển & Điện tử antenna is designed at frequency of 36 GHz, the bandwidth percentage is only under 6% [4] This bandwidth is not enough for applications at frequency band greater than 30 GHz This paper is going to present the x array antenna with improved parameters By using EBG structure, not only the gain of antenna is enhanced, but also the directivity and efficiency are improved In addition, by using multi substrate layer, the bandwidth of antenna is significantly improved The antenna is designed at frequency of 11 GHz and fabricated on FR4 substrate with thickness of 1.6 mm, εr = 4.4 and tanδ = 0.02 DESIGN OF ARRAY ANTENNA WITH EBG STRUCTURE a) Proposed Electromagnetic Band Gap Structure In the past, there was some papers which proposed EBG structures [1] [5] Based on these documents, the authors developed a new EBG structure The model and equivalent circuit of the proposed EBG structure are shown in Fig In here, the gaps between the conductor edges introduce equivalent capacitance C In addition, the narrow strips, connected the two patches, introduce equivalent inductance L [5] The size of cell is 42 x 42 mm The advantage of requiring no hole makes this EBG structure easy for fabrication In addition, the band gap feature of EBG structures has found useful applications in suppressing the surface waves in microstrip antenna designs a) b) Figure The proposed model of structure: EBG structure and equivalent circuit (a), Complementary-EBG structure and equivalent circuit (b) In here, the equivalent circuit is constructed as follows The each microstrip transmission line corresponds with a inductor while the band gap between two microstrip tranmission lines corresponds with a capacitor We know that the resonant frequency is given by: f re 2 LC (1) Then, the impedance of resonant LC circuit is calculated as follows Z 12 j L LC (2) N N Lan, T T Thao, V V Yem, “Gain and bandwidth enhancement … EBG structure.” Nghiên cứu khoa học công nghệ with 2 f The value of capacitor and inductor can be calculated by the following equations [1]: C W 1 r W g cosh 1 g (3) L h (4) g is the band gap between two adjacent EBG elements, W is the width of each EBG element ɛr is dielectric constant of metarial, ɛ0 is dielectric constant of vacuum, µ and h are the permeability and thickness of substrate, respectively b) Apply EBG to antenna To verify the proposed EBG structure, we will apply this structure to array antenna a) b) c) Figure The model of antenna with EBG (a), 4x4 array antenna (b), ground with EBG (c) The model of antenna is illustrated in Fig The proposed antenna model consists of an array antenna on top, first substrate, second substrate and ground with EBG structure at the bottom In this case, both the first and second substrates are FR4 with thickness of 1.6 mm, εr = 4.4 and tanδ = 0.02 Although FR4 have a high dielectric loss, FR4 is the most popular substrate in Vietnam because of economic effect and its popularity Therefore, the author selected FR4 substrate Table Parameters of EBG structure Parameters c cj w c2 lj lj lj Value 1 1.5 The array antenna includes 16 elements and 15 T-junction power dividers The size of each element is 15 x 12 mm while the distance between elements is approximately 32 mm (from center of antenna) The antenna is designed at frequency 11 GHz The size of antenna is 151 x 152 mm By using formulas in [6], we can calculate size parameters of antenna as follow In here, the width and length of patch are given by, respectively: c W f0 (5) r 1 Tạp chí Nghiên cứu KH&CN quân sự, Số 50, 08 - 2017 13 Kỹ thuật điều khiển & Điện tử L Leff 2L (6) in which: W 0.264) h W 0.258)( 0.8) h ( eff 0.3)( L 0.412h ( eff c Leff eff (7) (8) f reff r 1 r 1 10h 1 W 1/ (9) In which, ɛr and ɛeff are the dielectric constant and the effective dielectric constant of substrate, respectively; h is the thickness of substrate; f0 is the resonant frequency of antenna Finally, the size of an element is 15 x 12 mm while the width of microstrip line is given by equations[7]: Z0 If w/h < 1: While w/h > 1: Z0 120 60 eff 8h w ln w 4h (10) eff w w h 1.393 0.677 ln h 1.444 (11) In here, ɛeff is the effective dielectric constant In this case, the characteristic impedance of antenna is 50 Ohm, therefore, the width of microstrip line is approximately 3.05 mm In addition, to match impedance for power dividers, the quarter-wave transformers are used Then, the impedance of quarter-wave transformers is given by [8]: (12) ZT Z Z in where, Zin: Input impedance of line, Z0: Characteristic impedance To enhance bandwidth for antenna, this paper uses method of multiple substrate layers We know that the percentage of antenna bandwidth of is given by [9]: % BW In which: A = 180 if and A = 220 if 14 h 0 r h 0 r A h 0 r W L 0.045 , A = 200 if 0.045 (5) h 0 r 0.075 0.075 N N Lan, T T Thao, V V Yem, “Gain and bandwidth enhancement … EBG structure.” Nghiên cứu khoa học công nghệ From above formula, we can see that to increase bandwidth, we can rise the thickness of substrate by using multi dielectric layers SIMULATION AND MEASUREMENT RESULTS a) Simulation results To verify the proposed EBG strucutre, in this section, we compare antenna parameters when the antenna is based on: one substrate layer, multi substrate layer, multiple substrate layer with UP-EBG structure and with proposed EBG structure Fig shows the comparison between the reflection coefficient, gain and efficiency of antenna with UP-EBG strcuture [1] and proposed EBG structure, respectively It is clear that although the antenna bandwidth using UP-EBG structure is quite wide with approximately GHz, this bandwidth is also smaller than bandwidth using proposed EBG structure In addition, at the frequency of 11 GHz, the gain of antenna with UP-EBG is not high Moreover, although the efficiency of antenna with UP-EBG is quite high with 87%, this value is also lower than ones with proposed EBG structure (88%) This shows that the proposed EBG structure improves parameters of antenna better This is due to a suppressing the surface wave when EBG structure is used Therefore, the gain and efficiency of antenna are enhanced Fig illustrates the reflection coefficients and gains of antenna in three cases: One substrate layer, two substrate layers and two substrate layers with EBG a) b) c) Figure The comparison of antenna parameters between UP-EBG and the proposed EBG structure a) b) Figure The reflection coefficients (a) and gains (b) of antenna in three cases: one substrate layer, two substrate layers and two substrate layers with EBG From Fig 4(a), we can see that the bandwidth of antenna with one substrate layer and two substrate layers is only approximately 900 MHz and GHz, respectively While the bandwidth of antenna with two substrater layers and EBG is 1.4 GHz It is clear that the bandwidth of antenna is significantly improved when using EBG structure Moreover, the impedance matching of antenna is also improved We can see that through using multiple substrate, the bandwidth of antenna is also improved Moreover, using EBG structure creates consecutive cavity resonators and this leads to the fact that the bandwidth is Tạp chí Nghiên cứu KH&CN quân sự, Số 50, 08 - 2017 15 Kỹ thuật điều khiển & Điện tử enhanced dramatically From Fig 4(b), it is clear that the gain of antenna is the greatest at frequency of 11 GHz While in the other cases, the highest pick of the gain reaches at frequencies of 13 GHz and 10 GHz, respectively We can see that by using EBG structure, not only the bandwidth of antenna is improved, but also the gain of antenna is enhanced The current re-distribution helps the antenna to create many in-phase currents and this helps to reinforce the gain for antenna Fig shows the bandwidth, efficiency and gain of the proposed antenna while Fig illustrates radiation pattern of 3D and polar We can see that the bandwidth of antenna is 1.4 GHz and the percentage of antenna bandwidth is more 12.7% Normally, the bandwidth percentage of microstrip antenna is only 5-6% This shows that the bandwidth is remarkably improved Moreover, the gain and the efficiency of antenna are 11.4 dBi and 88%, respectively Normally, the efficiency of microstrip antenna is only 60% This shows that the efficiency of antenna is significantly improved b) a) Figure The parameters of the proposed antenna: reflection coefficients (a); gain and efficiency (b) a) b) Figure Radiation pattern: 3D (a) and polar (b) From Fig 6, we can see that the directivity of antenna is very high and the angular width of 3dB is very small (16.8 degree) In addition, the side lobe level is also small (-4.5 dB) Therefore, the antenna can satisfy well applications which require high directivity By using EBG structure on the ground plane, the surface current re-distribution for antenna is implemented and this leads to the fact that there is the enhancement of in-phase currents Therefore, the gain of antenna is improved b) Measurement results Fig illustrates the fabricated antenna based on FR4 thickness of 1.6 mm, εr = 4.4 and tanδ = 0.02 and the simulation and measurement results The size of antenna is 151 x 152 mm The antenna includes 16 elements and 15 power dividers The antenna model consists of an array antenna on top, first substrate, second substrate and ground with EBG structure at the bottom We can see that although there is a small difference between simulation and measurement results, the frequecy range for operation is still guaranteed Therefore, this result is acceptable In addition, the bandwidth of antenna is very large (2.5 GHz) 16 N N Lan, T T Thao, V V Yem, “Gain and bandwidth enhancement … EBG structure.” Nghiên cứu khoa học công nghệ corresponding to 22.7% of bandwidth percentage This bandwidth is wide enough for applications in X-band a) b) c) Figure The model of the fabricated antennna: Top (a), bottom (b) and the simulation and measurement results of antenna (c) Compared to some announced research results, we can see the followings In [10], the array antenna of 16 elements is designed frequency of 10.5 GHz, but the gain of antenna is only 10.3 dBi With applications in X band, this value of gain is too low In another research [11], the percentage of bandwidth is only 6% although the array antenna consists 16 elements and is designed at frequency 11 GHz This bandwidth is not large enough for applications in X band Similarly, the array antenna of 64 elements is designed at 60 GHz, but the efficiency of antenna is only 70% [12] With this efficiency, the antenna can not operate well CONCLUSIONS A new EBG structure is proposed in this paper and it is successfully applied for array antenna of x The antenna is designed at frequency of 11 GHz based on FR4 thickness of 1.6 mm, εr = 4.4 and tanδ = 0.02 By using new EBG structure, the parameters of antenna are improved such as bandwidth, gain, efficiency The proposed antenna has wide bandwidth (2.5 GHz for measurement result), high gain (11.4 dBi) and high efficiency (88%) The size of antenna is 151 x 150 mm while the distance between elements is 32 mm By limitting some disadvantages for microstrip technology through using proposed solution, the microstrip antenna becomes very useful With some advantages such as simple and easy fabrication and low cost, the proposed EBG structure can be widely applied REFERENCES [1] F Yang and Y Radmat-Samii, “Electromagnetic band gap structures in antenna engineering”, NY: Cambiridge Press, 2009 [2] A Mavaddat, S H M Armaki and A R Erfanian, “Millimeter-Wave Energy Harvesting Using 4x4 Microstrip Patch Antenna Array,” in IEEE Antennas and Wireless Propagation Letters, vol 14, no , pp 515-518, 2015 [3] L Wang, Y J Cheng, D Ma and C X Weng, “Wideband and Dual-Band High-Gain Substrate Integrated Antenna Array for E-Band Multi-Gigahertz Capacity Wireless Communication Systems,” in IEEE Transactions on Antennas and Propagation, vol 62, no 9, pp 4602-4611, Sept 2014 [4] B T P Madhav , V G K M Pisipati , S Susrutha Babu , S Suparshya, “K15 Liquid Crystal Substrate Based 4X4 Array Elliptical Patch Antenna Operating At 36 GHz Band,” International Journal of Recent Trends in Electrical & Electronics Engineering, Sept 2011, ISSN: 2231-6612 Tạp chí Nghiên cứu KH&CN quân sự, Số 50, 08 - 2017 17 Kỹ thuật điều khiển & Điện tử [5] Huynh Nguyen Bao Phuong, Dao Ngoc Chien, Tran Minh Tuan, “A Novel Compact Triple-Band Electromagnetic Bandgap (EBG) Structure,” International Journal of Advances in Engineering & Technology, Vol.5, Iss 2, pp 253-262 , 2013 [6] Constantine A Balanis, “Antenna theory - Analysis and Design,” 4th Edition, John Wiley & Son, INC, 2016 [7] Pozar, D M., “Microstrip Antennas: The Analysis and Design of Microstrip Antennas And Arrays”, IEEE Press, New York, USA, 1995 [8] David M Pozar, “Microwave Engineering,” 4th Edition, Wiley, 2012 [9] D G Fang, “Antenna Theory and Microstrip Antennas,” CRC Press 2009, ISBN: 978-1-4398-0739-2 [10] D Hua, S S Qi, W Wu and D G Fang, “CPW-Fed Printed Antenna Array With Conical Beam,” in IEEE Transactions on Antennas and Propagation, vol 64, no 3, pp 1096-1100, March 2016 [11] S Casas-Olmedo, J L Masa-Campos and P Sánchez-Olivares, “Design and characterisation model for a linearly polarised patch array fed by serial rectangular waveguide network,” in IET Microwaves, Antennas & Propagation, vol 8, no 14, pp 1204-1210, 11 18 2014 [12] Y Li and K M Luk, “A 60-GHz Wideband Circularly Polarized Aperture-Coupled Magneto-Electric Dipole Antenna Array,” in IEEE Transactions on Antennas and Propagation, vol 64, no 4, pp 1325-1333, April 2016 TĨM TẮT TĂNG CƯỜNG BĂNG THƠNG VÀ TĂNG ÍCH CHO ANTEN MẢNG BẰNG CÁCH SỬ DỤNG NHIỀU TẦNG ĐIỆN MÔI VÀ CẤU TRÚC EBG Ngày nay, công nghệ vi dải sử dụng rộng rãi ưu điểm kích thước nhỏ, trọng lượng nhẹ, chi phí thấp dễ dàng chế tạo Tuy nhiên, công nghệ vi dải đặt nhiều thách thức cho người thiết kế anten số nhược điểm chúng tăng ích hiệu suất thấp, băng hẹp Do đó, việc cải thiện tham số cho anten quan trọng cần thiết Một anten mảng x với tham số cải thiện cách sử dụng nhiều tầng điện môi cấu trúc EBG đề xuất báo Anten đề xuất có số ưu điểm: tăng ích cao (hơn 11.4 dBi) tỉ lệ phần trăm băng thông lớn (23% - 2.5 GHz cho kết đo lường) hiệu suất cao (88%) Bên cạnh đó, anten có độ định hướng cao mức búp sóng phụ thấp Anten thiết kế tần số trung tâm 11 GHz Anten mô chế tạo lớp điện môi FR4 với độ dày 1.6 mm, số điện môi 4.4 suy hao 0.02 Các kết mô thu từ phần mềm CST so sánh với kết đo Từ khóa: Anten mảng, Dải chắn điện từ (EBG), Nhiều tầng điện môi, Anten vi dải Nhận ngày 20 tháng năm 2017 Hoàn thiện ngày 31 tháng năm 2017 Chấp nhận đăng ngày 18 tháng năm 2017 Author affiliations: Hanoi University of Science and Technology; Posts and Telecommunications Institude of Technology *Corresponding author: nnlan@moet.edu.vn 18 N N Lan, T T Thao, V V Yem, “Gain and bandwidth enhancement … EBG structure.” ... Yem, Gain and bandwidth enhancement … EBG structure. ” Nghiên cứu khoa học công nghệ From above formula, we can see that to increase bandwidth, we can rise the thickness of substrate by using multi. .. cases: one substrate layer, two substrate layers and two substrate layers with EBG From Fig 4(a), we can see that the bandwidth of antenna with one substrate layer and two substrate layers is... MHz and GHz, respectively While the bandwidth of antenna with two substrater layers and EBG is 1.4 GHz It is clear that the bandwidth of antenna is significantly improved when using EBG structure