Microsoft Word - ETASR_V13_N1_pp10151-10157 Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 10151-10157 10151 www.etasr.com Ayari: On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis … On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis for 5G Wireless Communication Systems Mohamed Ayari Faculty of Computing and Information Technology, Northern Border University, Saudi Arabia | Syscom Laboratory, National Engineering School of Tunis, University of Tunis El-Manar, Tunisia mohamed.ayari@nbu.edu.sa (corresponding author) Received: 21 December 2022 | Revised: 5 January 2023 | Accepted: 7 January 2023 ABSTRACT The bandwidth demand in mobile wireless applications has grown at an astounding rate due to the fast evolution of technology, spurring the antenna design fields. The approaches associated with realizing antenna structure at mm-Wave frequency bands for future 5G cellular devices present advantages and disadvantages. This paper exhibits a fast and original approach based on the transverse wave formulation called-up Advanced Transverse Wave Approach (ATWA). A compact 5G patch antenna is designed, measured, simulated, and analyzed in the context of unlicensed mm-wave ISM-band applications. Compared to recently published works, the obtained result analysis proves the efficiency of the proposed method in terms of calculation accuracy, computational efficiency, and peak memory usage and the overall good performance of the proposed antenna. Keywords-5G antennas; advanced transverse wave approach; calculation accuracy, mm-wave analysis I. INTRODUCTION Nowadays, much research is directed at the fifth-generation mobile communications system (5G). Soon the traffic volume will be 1000 times over than the last decade with low cost and minimum power consumption, data rate communication will exceed 10Gbps making it 100 times faster than 4G, simultaneous connection of a large number of terminals will be available to support the future spread of M2M communications and internet of things (IoT), all thanks to the 5G technology. Undoubtedly, there are many challenges in this context, among them is to design, treat, and simulate mm-wave antennas used in 5G wireless in an effective way. Numerous recent scientific works have concentrated on the design and mm-wave investigation of 5G antennas with diverse size, from compact to large, either 2D or 3D [1-3]. Besides, 5G antenna shapes (i.e. circular, elliptical, rectangular, hexagonal, cross, etc.) [4-7] are considered as a significant parameter in the analysis process to achieve or not good quality in terms of performance and cost- effectiveness. In wireless communication systems, small patch antennas play an important role in the gain and bandwidth improvements due to features such as multiband properties, low profile topology and cost, good gain, and easy fabrication [8-10]. Several publications have been reported in this context. For instance, a compact size dual band patch antenna functioning at 10.15GHz and 28GHz for 5G mobile communications has been designed and studied in [11]. In [12], the authors presented a new capacitive coupled patch antenna array operating at the frequency band of 24-28GHz providing 360° coverage for 5G based smartphone services. In [13], a patch slotted antenna using FR4 substrate with the size of 18×18×1.6mm 3 providing at 10.15GHz a gain of 4.46dB and one of 6.6dB at 28GHz was reported in [14] using a small antenna with coplanar feeding for a Rogers RT5880 substrate and 5×5×0.254mm 3 size. Such antennas present low radiation efficiency, low gain, and some intricacy in the fabrication process. The mm-wave phased array 5G antenna which is running in the frequency range of 25 to 40GHz has been designed and analyzed in the context of Multiple-Input Multiple-Output (MIMO) applications. The increased demand of frequency allocation coerced the Federal Communication Committee (FCC) to boost more than 18GHz of spectrum surrounding the mm-wave frequencies [15, 43] in order to enhance the development and scientific research in 5G technology. However, the 57-71GHz interval which is the unlicensed frequency band according to FCC covers an important set of applications, such as WiGig [16], a new technology derived from Wi-Fi but supporting faster wireless transfer speed than WiFi. So, many recent publications have Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 10151-10157 10152 www.etasr.com Ayari: On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis … been reported in the context of analysis and design of 5G antennas used for WiGig applications. In [17], a stacked circular patch antenna with monopole type pattern was developed for 60GHz WPAN application. A 60GHz microstrip patch antenna was investigated in [18] based on different dielectric materials to prove their impact on antenna operation. In [19], the authors proved the efficiency of a 60GHz virtual loop antenna built on low resistivity silicon substrate. These antennas have been fabricated and designed in different shapes, such as rectangular, circular, helical [20], double F-slot [21], double U-slot [22], T-slot [23], E- and H-slots [24]. Moreover, the feasibility of 5G connectivity beyond 70GHz was demonstrated using an experimental prototype in [25]. The investigation and analysis of mm-wave 5G antenna based on numerical methods is an unprecedented and great challenge in the full-wave electromagnetic (EM) simulation sphere. Numerical EM methods belong to the core of the mm-wave analysis of 5G planar structures such as the Method Of Moments (MOM) [26], or its alternative Fast Multipole Method (FMM) [27], and the full spectrum method named Partial Element Equivalent Circuit (PEEC)[28] for solving integral equations of EM waves. In the same vein, Finite Element Method (FEM)[29], Finite Difference Time Domain (FDTD) method [30], and Finite Integration Technique (FIT) [31] belong to differential equation solvers. These numerical methods necessitate a significant amount in memory and processor power as well as high accuracy in features and design for full-wave and mm-wave analysis of planar structures employed in wireless systems [32]. In the area of wireless applications, the Advanced Transverse Wave Approach (ATWA) developed by our research team has significant benefits over previous numerical EM approaches in terms of speed, compactness, and memory consumption. To this purpose, we adapt and refine our ATWA approach to work with mm-wave 5G antenna simulations, and we tested its efficiency and stability in this setting. In line with the above mentioned works, an appropriate 5G antenna was considered and designed to validate our approach in the context of mm-wave 5G applications and offer the possibility to investigate smart and powerful antennas for the next generation of innovative wireless technology. In the following, we present and develop our numerical EM method –advanced transverse wave approach– in the context of mm-wave applications. II. ATWA: THEORETICAL BACKGROUND For most practical interest problems pertaining to EM radiation and scattering, an analytic solution of integral equations formulating the problem cannot be found. Therefore, researchers tend to utilize computational techniques to obtain a solution. We briefly present in this section the mathematical background and the theoretical foundation of the numerical EM method ATWA as well as its main characteristics and strong points. The two-dimensional transverse wave approach – a fast numerical method based on an iterative process– has several potentialities that set it apart from other computational EM approaches. There are no matrix inversion calculations in the TWA process, no constraints are required on the component forms, no numerical instabilities frequently arising from large matrices can be found, and the convergence is guaranteed independently of the interfaces of studied planar structures. In the following, we present a small theoretical background of our EM-approach 2D-ATWA for mmWave analysis of planar structures. The general integral relation linking the electric field to current density and considering the boundary and edge conditions on sub-domains characterizing the air-dielectric interface � can be written as follows: �(�, �) = (�, �, �� , �� )�(��, ��) �� ��� (1) where (�, �, ��, �� ) denotes the dyadic Green’s function [33]. Referring to the wave concept already investigated and developed in [36], the general equation linking the transverse electric field ET to the transverse magnetic field HT can be expressed as: ��,� = (4��� )������,� + (−1)���� ��,� � (2) where τ is a Boolean parameter referring to the wave nature (i.e. τ=0 for incident wave (W=A) and τ=1 for reflected wave (W=B)), the superscript T refers to the tangential components, and ��� stands for the wave impedance of the homogeneous isotropic region i ∈ {1,2} given by: ��� = � × "#$% &$%' ( ) *' (3) where � is the intrinsic impedance of free space defined as: � = 120- or 377Ω (4) where &$% , #$%, denote the relative permittivity (capacitivity) and relative permeability (inductivity) of the medium I and the vector JT is defined from the tangential magnetic field HT phased by π/2 from v which denotes the outgoing normal vector oriented towards region i. It can be written as: �� = .� × � (5) Overall, both incident (A) and reflected (B) waves can be associated through the following relation: /0 = 123 In modal domain3 = 450 + 3(�) In spatial domain (6) where 3(�)represents the general excitation wave on the source. Moreover, shifting from spatial to modal spaces is guaranteed by the transitional spectral space. In fact, at the discontinuity interface, the two-dimensional Fast Fourier Transform (2D-FFT) or the two-dimensional Non-Uniform Fast Fourier Transform (2D-NUFFT) [37-38] for uniform and non-uniform distribution, respectively, are intercepted in the transition between the spatial and spectral domains in order to accelerate the iterative process. The change from spectral to modal spaces can be ensured by the rotation of angle 6, given by: 6 = 789:;(<=>? <@>?' ) (7) Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 10151-10157 10153 www.etasr.com Ayari: On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis … Undoubtedly, the passing from modal to spatial domains is achieved by the inverse 2D-FFT or 2D-NUFFT as a first step and the rotation of angle−6 as the next step. The round trip from these spaces is repeated until the system’s convergence. The 2D-TWA can be accelerated by applying the anisotropic mesh technique [39] which calls the 2D-NUFFT to manage precisely the non-uniform discretization. Memory and computational complexity for both the Forward and Backward of the ATWA process is guaranteed at O(B� CD;B� ) time, where B� represents the meshing density applied to the structure to be analyzed, whereas the overall computational complexity of iterative solvers is O(B *), the same with MOM- and FEM-based solvers [40]. Table I recapitulates the iterative process of the ATWA approach, highlighting at each step the computational effort and the total time efficiency. TABLE I. ITERATIVE PROCESS AND COMPUTATIONAL EFFORT OF ATWA Step Description Complexity Init Computation of spectral-modal transition, reflection, and diffraction coefficients. Input complex vectors of bilateral excitation source (incident and reflected waves at t=0) B00 and A0=0. E(FG) 1 Application of 2D-FFT/2D-NUFFT at iteration k. E(FG HIJFG) 2 Application of modal transform at iteration k. E(FG) 3 Application of reflection operator at iteration k+1. E(FG) 4 Application of the inverse modal transform at iteration k+1. E(FG) 5 Application of the inverse of 2D-FFT/2D- NUFFT at iteration k+1 E(FG HIJFG) 6 Application of diffraction operator at iteration k+1. E(FG) 7 Compute current density, electric field, and input impedance Zin at iteration k+1. E(FG) 8 Test the convergence of Zin at iteration k+1. If Zin converges, then keep all EM quantities Else goto Step 1. E(FKLM) (B�NO ≪ B� : total number of pixels on the sub- domain source) III. ANTENNA DESIGN FOR 5G The new 5G demand can open prospects for miscellaneous new applications and the design process can be evolved taking into consideration these requirements. Against this background, a 5G small patch antenna fed by a microstrip line has been designed in the context of wireless applications (Figure 1). Such an antenna can enhance the radiation directivity and be used to fix and relay signals around obstacles in the context of ISM-band applications. The proposed planar structure is composed by an lp×wp radiating patch printed upon an ls×ps×hs substrate with Rogers 5880. RT/duroid 5880 laminate is considered as a judicious choice and a perfect substrate, since it is isotropic and characterized by the lowest electrical loss for reinforced polytetrafluoroethylene (PTFE) [34], uniform electrical properties over frequency, low moisture absorption, and excellent chemical resistance. This substrate is more convenient to mm-wave applications, military radar systems, commercial airline broadband, and missile guidance systems. Fig. 1. The proposed 5G small patch antenna fed by microstrip line. TABLE II. GEOMETRIC SIMULATION PARAMETERS OF THE PROPOSED 5G-ANTENNA Meshing resolution 512×512 Box dimensions (mm) QR = 8.192 �R = 8.192 Patch Length CS = 2.912 = 182 pixels Width TS = 3.2 = 200 pixels Microstrip line (mm) CO) = 2.56 = 160 pixels CO* = 0.96 = 60 pixels COU = 1.12=70 pixels TO = 0.736=46 pixels U-slot simensions (mm) CV = 1.12 = 70 pixels TV = 1.024 = 64 pixels Width WX (mm) TY = 0.192 = 12 pixels Source dimensions (mm) CZ = 0.736 = 46 pixels TZ = 1.792 = 112 pixels Form factor of source CZ TZ' = 0.41 Substrate Thickness [ = 130μm Type: Rogers RT/duroid Height h = 0.5mm In order to enhance the capacitance inhibiting the probe inductance which causes an expansion of the impedance bandwidth, the U-slot has been loaded on the patch. The U-slot technique has been applied in many recent 5G structures [15, 35] showing adeptness in wideband notion. The design parameters are detailed in Table II. IV. SIMULATION RESULTS AND DISCUSSION This section provides a concise and precise description of the experimental results, their interpretation, and the conclusions that can be drawn. In order to validate our numerical method in the EM simulation space of 5G antennas, we investigate the proposed planar structure shown in Figure 1 by analyzing the S11 parameter and comparing it with the results obtained in the literature. The simulation investigation was carried out by our EM simulator based on the ATWA method and developed in C++ environment. The modeling simulation constraints are given in Table III. The advanced TWA approach gives certain significant potentialities to the iterative scheme. It detaches the continuities relations defining the boundary conditions from the integral one, taking into consideration the half-spaces describing the different metallic interfaces identifying the proposed structure. One of these potentialities are the above mentioned Heaviside functions associated to the 5G-antenna (i.e. sub-domains: metallic .\]^_ = `a , dielectric .\]^_ = Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 10151-10157 10154 www.etasr.com Ayari: On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis … bc , source .\]^_ = 49a , and surface impedance .\]^_ =dZV$e ). The reflection coefficient or insertion parameter S11 is considered as the standard parameter for antennas. It quantifies the power reflected from the antenna and identifies the different resonance frequencies. The simulation result as depicted in Figure 2 shows the evolution of the S11 of our proposed antenna. TABLE III. MODELING SIMULATION PARAMETERS OF THE PROPOSED 5G-ANTENNA Modeling parameters Description Nature of box Periodic walls Type of polarization Bilateral in x-direction Number of iterations Nghij = 500 Value of surface impedance �� = 0 (surface impedance sub- domain is equivalent to metallic sub-domain) Permittivity of regions &$� = 1 &$� = 2.2 Waveband k>�? = 50GHz k>l= = 70GHz 4:am_k$o = 0.5Ghz Height ℎ� ℎ� = 0 (monolayer) Fig. 2. Evolution of S11 coefficient. Two bands have been detected at [57.62, 63.32] GHz and [64.29, 66.05] GHz, where the resonance frequencies are respectively depicted at 60.47GHz and 65.17GHz. The return losses are correspondingly -37.83dB and -12.44dB. The Fractional Bandwidths (FBWs) [36] are consequently 9.43% for the first and 2.7% for the second band of the proposed 5G- antenna. The Voltage Standing Wave Ratio (VSWR) is deduced at 1.0260dB for the 60GHz band which is considered as a good impedance for 5G wireless systems. The presence of double resonances is due to the U-slot loaded on the patch antenna that it is warranted by simulation result based on 2D- ATWA. Table III illustrates the comparison between the proposed 5G antenna and other known antennas. It is noticed that the three selected reference 60GHz antennas are simulated using the Finite-Element Method (FEM)-based Frequency Domain Solver (FDS) of CST Microwave Technology [41] and the FEM based high- frequency structure simulator (HFSS) of ANSYS [24, 42]. Besides, different simulation results of the proposed antenna based on our ATWA method are successfully presented such as the evolution of the impedance as a function of frequency (Figure 3), making evident the stability of the system around the resonance frequency, the 3D-radiation pattern (Figure 4), the azimuth pattern (Figure 5), and the elevation pattern (Figure 6) at 60GHz proving the high and accurate radiation directivity and gain of the proposed 5G antenna. Fig. 3. Evolution of the impedance as a function of frequency. Fig. 4. Radiation pattern at 60GHz. Overall, the obtained simulation results are in good agreement with the results of [24, 41, 42], with some preferences of our system in terms of size, multi-band notion, and impedance bandwidth. The computational statistics in terms of memory and CPU time for these simulations, using an Intel® Core™ i7-10875H Processor with 8 cores based on the Comet Lake architecture, are given in Table IV. The peak memory usage and total calculation time are significantly reduced in comparison with the other FEM-based solvers with the same computing resources. This proves the feasibility, plausibility, and EM-validity of our approach in 5G antenna simulations along with its accuracy and numerical stability in the compilation process. In addition, considering the above mentioned features as the efficiency of the AMT technique presented by our approach (ATWA), a good workspace can be opened to investigate miniaturized and sensible structures used for new 5G wireless technologies. 45 50 55 60 65 70 75 80 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 Frq(GHz) R e fl e c ti o n C o e ff ic ie n t (d B ) S11 Parameter Simulated Ref [23] Ref [35] Measured Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 10151-10157 10155 www.etasr.com Ayari: On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis … TABLE IV. COMPARISON BETWEEN THE PROPOSED 5G-ANTENNA AND REFERENCE ANTENNAS Antenna Parameter Proposed [24] [41] [42] Substrate RT/duroid 5880 RT/duroid 5880 RT/duroid 5880 RT/duroid 5880 Shape-slot U-slot E and H slots U-slot U-slot Size (mm 2 ) 8.192×8.192 8×8 7.5×9.5 7.5×9.5 Simulator Own simulator HFSS FDS HFSS Numerical EM method ATWA FEM FEM FEM Return loss (db) -37.83 -40.99 -37.5 -29.36 Single/multiband Double band Single band Double band Single band Impedance bandwidth (dB) 4)) ≤ −10 4)) ≤ −10 4)) ≤ −15 4)) ≤ −15 VSWR at 60GHz band (dB) 1.0260 1.0186 1.0270 1.038 Peak memory usage/GB 6.96 9.53 11.41 10.31 Fig. 5. Azimuth pattern at 60GHz. Fig. 6. Elevation pattern at 60GHz. V. CONCLUSIONS In this paper, a brief theoretical background and the mathematical foundations of our two-dimensional Advanced Transverse Wave Approach (2D-ATWA) has been presented and developed for mm-wave applications. A 5G small patch antenna with U-slot fed by microstrip line was presented and effectively designed taking into account the presence of the U- shaped slot etched in the radiating patch and the isotropic substrate RT/duroid 5880. The obtained simulations were validated, evaluated, and compared to various 60GHz reference antennas already simulated and investigated using the Finite Element Method-based Frequency Domain Solver and ANSYS HFSS. The results prove the EM-stability and efficiency of our approach in the context of mm-wave applications. Many antenna parameters such as shape, size, embedded shape-slots and slits, substrate material, dimensions, etc. have great impact on the operation of an antenna, such as increasing/decreasing bandwidth and gain or generating single or multiband frequencies. 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Baudrand, "On the Use of Anisotropic Mesh Technique (AMT) in Transverse Wave Approach (TWA) for the EM Analysis of Microwave Circuits in Wireless Applications," in Symposia and Workshops on Ubiquitous, Autonomic and Trusted Computing, Brisbane, QLD, Australia, Jul. 2009, pp. 246– 251, https://doi.org/10.1109/UIC-ATC.2009.8. [40] S. Zuo, D. Garcia Donoro, Y. Zhang, Y. Bai, and X. Zhao, "Simulation of Challenging Electromagnetic Problems Using a Massively Parallel Finite Element Method Solver," IEEE Access, vol. 7, pp. 20346–20362, 2019, https://doi.org/10.1109/ACCESS.2019.2896615. Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 10151-10157 10157 www.etasr.com Ayari: On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis … [41] H. Liu, Y. He, and H. Wong, "Printed U-slot patch antenna for 60GHz applications," in International Workshop on Electromagnetics, Applications and Student Innovation Competition, Kowloon, Hong Kong, Aug. 2013, pp. 153–155, https://doi.org/10.1109/iWEM.2013. 6888796. [42] G. Kumar and C. Kumar, "Design and analysis of u-slot mircostrip patch antenna for mobile communication at 60 ghz," Acta Technica Corviniensis - Bulletin of Engineering, vol. 13, no. 1, pp. 35–38, 2020. [43] S. Ahmad et al., "Design of a Tri-Band Wearable Antenna for Millimeter-Wave 5G Applications," Sensors, vol. 22, no. 20, Jan. 2022, Art. no. 8012, https://doi.org/10.3390/s22208012. AUTHOR PROFILE Mohamed Ayari –received the Dipl.-Ing., M.S., and Ph.D. degrees in Telecommunications in 2003, 2004, and 2009, respectively, from the National Engineering School of Tunis (ENIT), Tunisia, in collaboration with the National Polytechnic Institute of Toulouse, France, and Virginia Tech, USA. He has been teaching at several universities since 2003. He has been a permanent research member at the 6'COM laboratory at ENIT from 2003. In 2005, he joined RCEM-Inc. in Toulouse, France. Since 2010, he has been a tenure-track Associate Professor at the National Engineering School of Carthage (ENICAR), Carthage University, Tunisia. In 2015, he joined the IT Department of the Faculty of Computing and Information Technology, Northern Border University (NBU), Kingdom of Saudi Arabia, as an Assistant Professor. His current research interests are electromagnetic (EM) fields, numerical EM methods, and computer-aided design of microwave circuits and antennas. His research interests also include information security, image processing and wireless applications.