This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 1Date of publication xxxx 00, 0000, date of current version xxxx 00, 0000. Digital Object Identifier 10.1109/ACCESS.2017.Doi Number Wideband Monopole Eight-Element MIMO Antenna for 5G Mobile Terminal Anju Kumari Rai1, Member, IEEE, Rahul Kumar Jaiswal1, Member, IEEE, Kahani Kumari1, Member, IEEE, Kumar Vaibhav Srivastava1, Senior Member, IEEE, Chow-Yen-Desmond Sim2, Senior Member, IEEE 1 Electrical Engineering Department, Indian Institute of Technology, Kanpur, 208016, India Electrical Engineering Department, Feng Chia University, Taichung, 407, Taiwan 2 Corresponding author: Anju Kumari Rai (e-mail: anjukumarirai@gmail.com), Chow-Yen-Desmond Sim (e-mail: cysim@fcu.edu.tw). This work was supported in part by the Ministry of Science and Technology (MOST), Taiwan, under project no. MOST 111-2221-E-035-022. It was also partly supported by Science and Engineering Research Board, India, under project no. CRG/2021/000376. ABSTRACT An eight-element wideband multiple-input multiple-output (MIMO) antenna for the fifthgeneration (5G) mobile terminal is proposed. The antenna elements are placed along both long side edges of the mobile terminal with a profile of 6 mm. The proposed monopole-inspired antenna element shows a good impedance match, isolation, and diversity parameter across a very wide bandwidth of 78 % (3.2-7.3 GHz), and it can cover the 5G NR n77/n78/n79/n96, LTE 46, and WLAN 5 GHz bands. The result shows that the MIMO antenna can offer inter-element isolation better than 12 dB, envelope correlation coefficient (ECC) below 0.069, and a peak channel capacity of 42.7 bps/Hz across the desired 5G bands. The specific absorption rate (SAR) analysis of the proposed MIMO antenna with a human head has exhibited SAR levels (0.41 W/Kg and 0.33 W/Kg at two resonating frequencies 3.9 GHz and 5.8 GHz, respectively) much lower than the Federal Communications Commission (FCC) permissible limit (1.6 W/Kg over 1 gram tissue). INDEX TERMS 5G mobile , MIMO antenna, specific absorption rate (SAR), sub-6 GHz, wideband. I. INTRODUCTION In the course of development in wireless cellular technology, fifth-generation (5G) communication systems are adopted to provide low latency and high data rate experience for network users [1]. Antennas are an essential component of wireless technology. Their application in 5G communication is highly dynamic depending upon different specific requirements such as broad bandwidth [2-3], polarization agility, reconfigurability [4], etc., along with common basic parameters. To satisfy the large throughput requirement for a 5G mobile terminal, a multiple antennaelement based MIMO antenna array is employed in the mobile terminal, which leads to the three main aspects of the 5G mobile terminal MIMO antenna, namely, antenna placement, bandwidth, and compatibility for users. In the existing literature [5]-[7], the earlier generation antennas are generally placed at the two extremes (top and bottom section) of the mobile terminal. To further integrate the 5G antenna array into the mobile terminal, the prospective 5G array is generally collocated along the longer edges of the smartphone frame to be compatible with pre-existing antennas [8]-[20]. As the 5G spectrum has stretched from its initial New Radio (NR) bands n77/n78/n79 (3.3-5.0 GHz) to the wireless local-area network (WLAN) 5GHz (5.15-5.825 GHz) bands [21], it is noteworthy that the NR-unlicensed (NR-U) bands of up to sub-7 GHz, known as n96 (5.925-7.125 GHz) have also been introduced recently [22]. Therefore, it is vital to satisfy the global 5G NR spectrums requirement by designing a wideband antenna array. In [8]-[13], MIMO antennas (with four- or eight-elements) have been investigated to support a fraction of sub-6 5G NR bands. To further cover the entire 5G sub-6 GHz, dual-band operating eight-element MIMO antenna arrays have also been studied [14]-[18]. Maintaining good isolation is an implicit term in MIMO antenna system. To achieve desirable isolation between the adjacent array elements of the MIMO antenna, connecting lines or slot etching techniques have been introduced [11]-[15]. However, the works above have VOLUME XX, 2017 1 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 indicated that it is difficult to realize a good isolation level without using any extra decoupling structure. To cover the entire 5G NR band n77/n78/n79, LTE band 46, WLAN 5G band, and 5G NR-U band n96, now referred to as the bands of interest (3.3-7.125 GHz), [19] has introduced an open slot-loaded metal rim 8-antenna MIMO array that can cover the bands of interest with isolation >11 dB. Subsequently, a 4-antenna MIMO array comprised of 2 PIFA pairs has also been developed with a wide bandwidth of 78% (3.3-7.5 GHz), but it has an isolation of >10 dB [20]. Notably, the profile of antenna configuration for mobile terminal discussed in [8]-[10], [16], [17], [18] is in order of 7 mm or more. As the average thickness of a flagship smartphone is about 0.35 inches (8.93 mm), its designated array antennas should have a profile (antenna height) of no more than 6 mm. To achieve such a profile, [12]-[15] have applied the technique of using either surface mount devices (SMDs) or defected ground structure method, but at the cost of design complexity. Nevertheless, achieving wide bandwidth, good isolation, and diversity performance parameters with low-profile characteristics for a large MIMO array is challenging. Therefore, the design of the proposed MIMO antenna array that is simple in structure and presents no fabrication complexity for the upcoming 5G environments without compromising the antenna array performances is imperative to the antenna industry. This paper proposes an eight-element MIMO antenna array with wide 6-dB impedance bandwidth of 78% (3.2-7.3 GHz) across the bands of interest, and it has exhibited good isolation of >12 dB without introducing the extra decoupling structure. Besides showing a low profile of only 6 mm, the proposed antenna array has also demonstrated good MIMO performance with desirable radiation patterns. Finally, the SAR analysis considering a mobile terminal with a human head to guarantee the user compatibility of the proposed antenna array is conducted. This manuscript is organized as follows. Firstly, the geometrical configuration of the proposed wideband eightelement MIMO antenna, along with its design evolution steps and working principle of operation, are discussed in section II, followed by simulated and experimental results in section III. Finally, section IV concludes the paper. II. ANTENNA DESIGN AND WORKING PRINCIPLE A. ANTENNA GEOMETRY Figures 1(a) and 1(b) depict the detailed geometry of the single antenna element and the layout of the proposed MIMO antenna, respectively. The proposed MIMO antenna is designed on FR4 substrates having a thickness of 0.8 mm, dielectric constant of 4.4, and loss tangent of 0.02. The antenna element is a rectangular monopole-inspired antenna; its feeding structure is a microstrip line of width 2.2 mm fed with an SMA connector. The overall dimension of each antenna element is 21.5 mm × 5.2 mm. The system ground plane has a FIGURE 1. (a) Detailed geometry of single antenna element with the design parameters (unit: mm): l1 = 21.5, l2 = 9.5, l3 = 0.9, w1 = 5.2, w2 = 4, w3 = 1 (b) layout of the proposed eight-element MIMO antenna. dimension of 150 mm × 72.6 mm printed on an FR4 substrate (150 mm × 75 mm). The clearance between the outer edges of the ground plane and substrate is 1.2 mm on each side. The two-reserved regions (#A and #B) of dimensions 15 mm × 75 mm are for the placement of main and diversity antennas (3G/4G/WLAN/WiFi etc.). The proposed antenna elements are printed on the inner surface of two standing FR4 substrates (150 mm × 5.2 mm) along the longer side edges of the ground, which can be considered as the smartphone frame. Therefore, the proposed MIMO antenna is compatible with a 6 mm sleek mobile terminal. Here, the proposed eight-element MIMO antenna is subdivided into two 1 × 4 arrays (ANT 1-ANT 4 and ANT 5-ANT 8), which are symmetric along the center of the system ground. The gap between ANT 1 and ANT 2 is d1 = 11.2 mm, and the gap between ANT 2 and ANT 3 is d2 = 11.6 mm. B. DESIGN EVOLUTION OF PROPOSED ANTENNA ELEMENT AND ITS WORKING PRINCIPLE The proposed MIMO antenna design is inspired by a rectangular monopole antenna to achieve wide impedance bandwidth. The impedance bandwidth can be significantly increased by reducing the width of the square monopole antenna [23]. The design evolution phases of the single element (ANT) and their reflection coefficients are shown in Fig. 2. Section 1 is a conventional rectangular monopole antenna of a length slightly greater than a quarter-guided wavelength corresponding to its resonance frequency (5.8 GHz). To excite a lower resonance frequency of the 5G NR bands, a rectangular monopole antenna with an L-shaped open slot is designed at 3.9 GHz resonance, which is now denoted as Section 2. Here, one can see that Section 1 is designed to cover NR n79/n96, LTE 46, and WLAN 5 GHz 2 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 bands, while Section 2 covers NR band n78. Therefore, to achieve a very wide bandwidth of 78% (3.2-7.3 GHz), it is realized that these two Sections (1 and 2) designed at two different resonance frequencies can be merged, which is denoted as the proposed Ant element. Notably, the impedance bandwidth at the lower band is further improved by optimizing the feedline length. Finally, the proposed ANT element can cover the entire 5G NR n77/n78/n79/n96, LTE 46, and WLAN 5 GHz bands. FIGURE 4. Transmission coefficients of (a) configuration A. (b) configuration A’ FIGURE 2. Design evolutionary phases of single element with design parameters (unit: mm): l1 = 21.5, l2 = 9.5, l3 = 0.9, l4 = 14.5, l5 = 11.1, w1 = 5.2, w2 = 4 and their reflection coefficient. To validate the performances of the proposed MIMO antenna, the current distribution across the ANT 1 element at two resonance frequencies, namely, f1 (3.9 GHz) and f2 (5.8 GHz), are depicted in Figs. 3(a) and 3(b), respectively. As depicted in Fig. 3(a), it can be inferred that Section 2, along with a portion of Section 1, is responsible for exciting the first resonance at 3.9 GHz. Similarly, from Fig. 3(b), the rectangular monopole portion of Section 1 is responsible for the excitation of the 5.8 GHz resonance. III. RESULT AND DISCUSSION A prototype of the proposed MIMO antenna was fabricated, and it is shown in Fig. 4. Measured results validate the simulated results. The S-parameter is measured using the N5222A PNA network analyzer (Agilent Technologies), and the far-field parameters are measured in a standard anechoic chamber. FIGURE 3. Current distributions along ANT 1 (a) 3.9 GHz (b) 5.8 GHz. The orientation of elements and spatial diversity technique are simultaneously used to maintain isolation among antenna elements. The antenna element is a combination of two sections resonating at different frequencies; thus, adjacent antenna elements (except ANT 2 - ANT 3 and ANT 6 - ANT 7 pairs to maintain symmetry) are placed in back-to-face orientation to suppress the coupling. The two possible configurations and their simulated transmission coefficients response are shown in Fig. 4. It is observed that configuration A exhibits better isolation level with respect to configuration A’. Thus, the antenna elements are placed in accordance with configuration A. FIGURE 5. The fabricated prototype (a) top view (b) bottom view (c) side view. 3 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 A. MATCHING AND ISOLATION FIGURE 6. Reflection coefficients of ANT 1-4 (a) simulated (b) measured. To verify that the proposed smartphone antenna has good MIMO performances, the diversity parameter (ECC) of ANT 1-4 is calculated from the far field three-dimensional (3-D) Efield patterns, considering the uniform multipath environment of balanced polarization. Fig. 7(a) shows the calculated ECC values across the desired bands of interest, which are well below 0.069. This result satisfies the acceptable ECC threshold (< 0.3) for the MIMO antenna [24]. The channel capacity of the eight-element MIMO antenna is also calculated and plotted in Fig. 7(a). It is obtained from the simulated results by averaging 1,00,000 independent identically distributed (IID) Rayleigh fading channel realization with a 20dB signal-to-noise ratio (SNR) [25]. Here, a channel capacity of > 39.5 bps/Hz (with a peak value of 42.72 bps/Hz) is observed, and it is comparable to the channel capacity of an ideal 8 × 8 MIMO antenna (46 bps/Hz). FIGURE 7. Transmission coefficients of ANT 1-4 (a) simulated (b) measured. The simulated and measured reflection coefficients of ANT 1-4 are plotted in Figs. 5(a) and 5(b), respectively. The results for ANT 5-8 are not shown for brevity. Here, the simulated 6-dB stacked impedance bandwidth was 77% (3.2 7.2 GHz), and the measured one was 78% (3.2-7.3 GHz), and they can well cover the 5G NR n77/n78/n79/n96, LTE 46, and WLAN 5G bands. The simulated and measured isolation levels between antenna elements (ANT 1-4) printed on the same side edge are shown in Figs. 6(a) and (b), respectively. Here, a desirable isolation level of better than 12 dB is achieved. The worst isolation is among ANT 2 and ANT 3 at the lower desired frequency range due to the Face-to-Face configuration to maintain structural symmetry as per practical requirements. In contrast, isolation of better than 12 dB is achieved. FIGURE 9. Simulated and measured radiation patterns of ANT 1 at 3.9 GHz and B. MIMO PERFORMANCE, EFFICIENCY AND RADIATION PATTERNS FIGURE 8. (a) Calculated ECC and channel capacity (b) simulated and measured total efficiency. 5.8 GHz across the xz and yz planes. Fig. 7(b) shows the simulated and measured total efficiency by exciting only antenna element ANT 1 (while the others were terminated to 50Ω loads) of the proposed MIMO antenna. Across the bands of interest, the simulated efficiencies ranged from 61% to 77%, whereas the measured ones were slightly lower, between 51% and 70%. The differences between the two results could be due to slight fabrication errors and tolerances Figs. 8 and 9 depict the simulated and measured radiation patterns of ANT 1 and ANT 2, respectively, at both resonance frequencies (3.9 GHz and 5.8 GHz), while all the other antenna elements are terminated to 50Ω loads. By observing these two figures, one can see that majority of Eθ radiation is 4 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 inclined towards the negative x direction. Thus, the direction of the main beam radiation of ANT elements is pointing away from the system, allowing good MIMO performance. FIGURE 12. (a) Reflection Coefficient and (b) Transmission Coefficient in single hand operation. FIGURE 10. Simulated and measured radiation patterns of ANT 2 at 3.9 GHz and FIGURE 13. (a) Reflection Coefficient and (b) Transmission Coefficient in two 5.8 GHz across the xz and yz planes. hand operation. C. USER’S HAND EFFECT AND SAR ANALYSIS In this case, the commercial software HFSS (high frequency structure simulator) are used to analyse the proposed antenna system with inclusion of human hand phantom in two different hand held situations, namely, single hand operation (SHO, data mode) and two hand operation (THO, read mode), as depicted in Figs. 11(a) and (b), respectively. The simulated Sparameters in single hand operation (SHO, data mode) and two hand operation (THO, read mode) are depicted in Fig. 12 and Fig. 13, respectively. Transmission coefficients of S21S81 (port 1 with other ports) and S23 are evaluated because of symmetry. FIGURE 11. Simulated model of proposed antenna with a user’s hand in (a) single hand operation and (b) two hand operation. FIGURE 14. Simulated total efficiency of antenna system in single hand and two hand operations. In SHO and THO condition, the impedance matching of ANT 6 and (ANTs 5 and 8), respectively, are highly affected, in spite that each antenna elements are able to cover the desired 5G bands with isolation level greater than 11 dB and 10 dB in the SHO and THO, respectively. The simulated total efficiency of the antenna system in both hand held situations are shown in Fig. 14. The total efficiency under SHO and THO are greater than 58% and 32%, respectively, whereas the simulated total efficiency of proposed antenna system is greater than 61%. This is because the hand tissues can absorb electromagnetic radiation energy, causing the deterioration of antenna efficiencies. However, the 5 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 simulated total efficiencies are still higher than 20%, which are acceptable for 5G smartphone MIMO system with the hand presence. Along with the effects of user’s hand on antenna performance, the biological implication on the users are also indispensable. The specific absorption rate (SAR) can be related to the electric field at a point in the human body, as denoted in (1) [26], 2 SAR = σ E field ρ (1) where σ is the conductivity of the tissue (S/m), ρ is the density of the tissue (kg/m3), and Efield is the root mean square value of the electric field strength in tissue (V/m). To validate the deplorability of the proposed MIMO antenna in a 5G user terminal (smartphone), the SAR analysis of the MIMO antenna while held against the ear is investigated. The main reason for such evaluation is that the human ear/brain could be affected (by high radiation) when the mobile terminal is in a talk position. Here, the MIMO antenna array is kept 2 mm away from the human head voxel, while each antenna element is excited with 25 mW. Figs. 10(a) and 10(b) depict the front, and side views of the SAR field values averaged over the simulated-tissue human head model at 3.9 GHz and 5.8 GHz, respectively. As the peak SAR values are 0.41 w/kg and 0.33 w/kg at f1 (3.9 GHz) and f2 (5.8 GHz), respectively, they are significantly lower than the FCC permissible SAR limit (1.6 W/kg over 1 gram tissue) [27]. wideband (covering up to 6 GHz and 7.125 GHz) designs for 5G mobile applications. TABLE 1. PERFORMANCE COMPARISON WITH EXISTING DESIGNS THAT COVER UP TO 6 GH Z AND 7.125 GH Z Ref. Profile Profile Isolation ECC PCCMIMO (GHz) (mm) [16] 3.1-6* 7 10 0.1 398 [17] 3.27-5.92# 7 12 0.1 43.938 [18] 3.3-6* 6 11 0.12 408 [19] 3.3-7.1* 7 11 0.09 39.88 [20] 3.3-7.5* 7 11 0.05 NA This work 3.2-7.3* 6 12 0.069 42.78 Ref.: Reference, ECC: Envelope correlation coefficient, Pcc: Peak channel capacity, *: 6 dB impedance bandwidth, #: 10 dB impedance bandwidth, Na: Not available. By observing the table, it is evident that the proposed MIMO antenna covers the required 5G NR bands of interest (3.37.125 GHz) while maintaining good isolation levels of > 12 dB, ECC values of < 0.069, and peak channel capacity of up to 42.7 bps/Hz. By observing [16]-[18], they have a profile of 7 mm and cannot cover the 5G NR band n96. Even though [19] has realized the desired 5G NR bands of interest, it was achieved by loading large dimension slots into the system ground plane, which is not encouraged for practical mobile applications. As for the one reported in [20], it is suitable only for a 4 × 4 MIMO antenna array arrangement, thus failing to fulfill the promise of high channel capacity requirement for 5G applications. In contrast, the proposed eight-element MIMO antenna can cover from 3.2 to 7.3 GHz without compromising another performance parameter. It also fulfills sleek mobile phone demand with a profile of only 6 mm. Furthermore, it has exhibited desirable isolation without loading any additional decoupling element. IV. CONCLUSION FIGURE 15. SAR field at resonance frequencies (a) at 3.9 GHz (b) at 5.8 GHz. An eight-element MIMO antenna has been successfully verified. The proposed wideband MIMO antenna can cover the entire 5G NR n77/n78/n79/n96, LTE 46, and WLAN 5 GHz bands with isolation greater than 12 dB. Besides exhibiting a desirable ECC of less than 0.069, it has also achieved a peak channel capacity of 42.7 bps/Hz. The SAR study of the proposed MIMO antenna was carried out to examine the interaction between the human head and the designed MIMO array. The results have shown acceptable average SAR values within the FCC permissible limit. Therefore, the proposed MIMO antenna array is a good candidate for a future slim 5G mobile terminal. D. COMPARISON REFERENCES Table 1 presents the performance comparison between the proposed MIMO antenna and those reported ones with [1] [2] J. G. Andrews et al., “What will 5G be?,” IEEE J. Sel. Areas Commun., vol. 32, no. 6, pp. 1065-1082, Jun. 2014. R. -S. Chen, G. -L. Huang, S. -W. Wong, M. K. T. Al-Nuaimi, K. W. Tam and W. -W. Choi, "Bandwidth-Enhanced Circularly6 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. 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Srivastava, “Fiveport MIMO antenna for n79-5G band with improved isolation by diversity and decoupling techniques,” J. Electromagn. Waves Appl., vol. 36 no.4, pp.542-556, Sept. 2021. B. Owen, “Regulatory reform: The telecommunications act of 1996 and the FCC media ownership rules,” SSRN Electron. J., 2003. 7 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in IEEE Access. This is the author's version which has not been fully edited and content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2022.3232698 ANJU KUMARI RAI received the B. Tech degree in Electronics and Communication Engineering from University College of Technology, Jharkhand, India, in 2016, and the M. E. degree in Microwave Communication in the year 2018 from the Birla Institute of Technology, Mesra, India. Her thesis was on Filter design over Folded Substrate Integrated Waveguide. Currently, she is pursuing a Doctor of Philosophy (PhD) in RF & Microwaves discipline in the Electrical Engineering department of the Indian Institute of Technology (IIT) Kanpur, India. Her research interests include MIMO antennas, 5G and beyond antennas. RAHUL KUMAR JAISWAL received the B. Tech degree in Electronics and Communication Engineering from Uttar-Pradesh Technical University, Lucknow, India, in the year 2012. He worked as a Project Trainee in Society for Applied Microwave Electronics Engineering and Research (SAMEER) Kolkata in 2015-16. He has completed his M. Tech degree in Microwave Electronics in the year 2016 from the University of Delhi South Campus, Delhi, India. He also worked as a Scientist in Institute for Plasma Research (IPR) Gandhinagar, India, in 2016-17. Presently, he is pursuing a Doctor of Philosophy (PhD) in RF & Microwaves discipline under the supervision of Prof. Kumar Vaibhav Srivastava in the Electrical Engineering Department at the Indian Institute of Technology Kanpur, India. Currently, he is serving as a Chair of IEEE APS-SBC at IIT Kanpur, India. He has published several journal/conference papers on various aspects of antennas and RF waveguides. He received IEEE Antennas and Propagation Society Doctoral Research Grant in 2021. His research interests include MIMO antennas, circularly polarized antennas, unidirectional and bidirectional endfire CP antennas, base station antennas, and full-duplex antennas. KAHANI KUMARI received the B. Tech degree in Electronics and Communication Engineering from West Bengal University of Technology, Kolkata, India, in 2012, and the M. E. degree in Microwave Communication in the year 2015 from the Indian Institute of Engineering Science and Technology, Shibpur, India. Currently, she is pursuing a Doctor of Philosophy (PhD) in RF & Microwaves discipline in the Electrical Engineering department of the Indian Institute of Technology (IIT) Kanpur, India. She has published several journal/conference papers on various aspects of full-duplex antennas and circularly polarized antennas. Her research interests include full-duplex antennas, MIMO antennas, circularly polarized antennas, unidirectional and bidirectional endfire CP antennas and base station antennas. KUMAR VAIBHAV SRIVASTAVA received the B.Tech. degree in Electronics Engineering from Kamla Nehru Institute of Technology, Sultanpur, India, in 2002, and the M.Tech. and Ph.D. degrees both in Electrical Engineering from Indian Institute of Technology Kanpur, Kanpur, India, in 2004 and 2008, respectively. He was with the GE Global Research Centre, Bangalore, India, for one year in 2008. In 2009, he joined as an Assistant Professor with the Department of Electrical Engineering, IIT Kanpur, where he is currently serving as a Professor since November 2018. His extensive research interests are microwave antennas, metamaterials, metamaterial absorbers and cloaking, FDTD technique, and MIMO Antennas. He has published more than 115 international journal papers, two international patents and 150 conference papers in the last fifteen years. Dr. Srivastava received various national and best paper awards. He was Chairperson of IEEE UP Section in 2018 and founding Chair of IEEE Antenna and Propagation Society Chapter in UP Section. CHOW-YEN-DESMOND SIM (M’07– SM’13) was born in Singapore in 1971. He received the B.Sc. degree from the Engineering Department, University of Leicester, U.K., in 1998, and the Ph.D. degree from the Radio System Group, Engineering Department, University of Leicester, in 2003. From 2003 to 2007, he was an Assistant Professor with the Department of Computer and Communication Engineering, Chienkuo Technology University, Changhua, Taiwan. In 2007, he joined the Department of Electrical Engineering, Feng Chia University (FCU), Taichung, Taiwan, as an Associate Professor, where he became a Full Professor in 2012 and as a Distinguish Professor in 2017. He has served as the Executive Officer of Master’s Program with the College of Information and Electrical Engineering (Industrial Research and Development), the Director of Intelligent IoT Industrial Ph.D. Program between August 2015 and July 2018. He co-founded the Antennas and Microwave Circuits Innovation Research Center in Feng Chia University and served as the Director between 2016 and 2019. He has served as the Head of Department of Electrical Engineering in Feng Chia University between 08/2018 and 07/2021. He has authored or coauthored over 170 SCI papers. His current research interests include antenna design, VHF/UHF tropospheric propagation, and RFID applications. He is a Fellow of the Institute of Engineering and Technology (FIET), a Senior Member of the IEEE Antennas and Propagation Society, and a Life Member of the IAET. He has served as the TPC Member of many international conferences, and has also served as the TPC Sub-Committee Chair (Antenna) of the ISAP 2014 and PIERS 2017/2019. He was invited as the Workshop/Tutorial Speaker in APEMC 2015, iAIM 2017, InCAP 2018, and the Invited Speaker of TDAT 2015, iWAT 2018, APCAP 2018, ISAP 2019, InCAP 2019, ISRAST 2020, and URSI GASS 2021. He was the Keynote Speaker of SOLI 2018, ISRAST 2020, and NEAST 2020. He has served as the Advisory Committee of InCAP 2018/2019 and ICoICCS 2021, and has also served as the TPC Chair of the APCAP 2016, iWEM 2019/2020. He is now serving as the General Co-Chair of ISAP 2021. He has served as the Chapter Chair of the IEEE AP-Society, Taipei Chapter (from 01/2016 to 12/2017), and he is the founding Chapter Chair of the IEEE Council of RFID, Taipei Chapter (from 10/2017 to 12/2020). He has served as the AE of IEEE Access between 08/2016 and 01/2021. He is now serving as the Associate Editor of IEEE AWPL, IEEE Journal of RFID, and (Wiley) International Journal of RF and Microwave Computer-Aided Engineering. Since October 2016, he has been serving as the technical consultant of SAG (Securitag Assembly Group), which is one of the largest RFID tag manufacturers in Taiwan. He is also serving as the consultant of Avary (the largest PCB manufacturer in mainland China) since August 2018. He was the recipient of the IEEE Antennas and Propagation Society Outstanding Reviewer Award (IEEE Transaction Antennas and Propagation) for seven consecutive years between 2014 and 2020. He has also received the Outstanding Associate Editor Award from the IEEE Antennas Wireless and Propagation Letters in July 2018. 8 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/
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