This work describes the design and analysis of a four-element wideband circularly polarized (CP) Multiple-Input-Multiple-Output (MIMO) antenna for mid-band 5G utilizations. The proposed MIMO antenna miniaturization is obtained by the implementation of composite right/left-handed (CRLH) transmission line (TL) and loading of octagonal shaped slotted rings inside the antenna ground plane. Further, the circular polarization radiation is obtained due to the sequence arrangement of two CRLH-TL based unit cells of opposite branches, inside a conventional square patch. The intended MIMO antenna encompasses two layers, the layer-1 consists of a four-element CRLH-TL based circularly polarized MIMO antenna placed in side-by-side configuration. The layer-2 consists of 3×3 square-shaped metasurface on one side and an octagonal slotted ring on another side. The combination of two layer results in wider bandwidths of 68.84% (2.21-4.53) and 3 dB axial ratio (AR) bandwidth of 30.4% (3.1-4.21 GHz). Furthermore, the antenna has better than 10 dB isolation, a maximum gain of 7.2 dBi at 4.04 GHz, radiation efficiency of more than 65%, and lower envelope correlation coefficient (ECC) values across the whole operating band. Diversity Gain (DG) values are high and near to 10 dB. Total Active Reflection Coefficient (TARC) and Channel Capacity Loss (CCL) values are also very much acceptable. As a result, the suggested four-element MIMO antenna is appropriate for midband 5G utilizations.
2. Kim, J., "Study on an epsilon-negative zeroth-order resonator antenna properties for mobile handsets," Microwave and Optical Technology Letters, Vol. 54, No. 4, 1066-1069, April 2012.
3. Ameen, M. and R. K. Chaudhary, "Electrically small circularly polarized antenna using vialess CRLH-TL and fractals for L-band mobile satellite applications," Microwave and Optical Technology Letters, Vol. 62, No. 4, 1686-1696, April 2020.
4. Park, B. and J. Lee, "Omnidirectional circularly polarized antenna utilizing zeroth-order resonance of epsilon negative transmission line," IEEE Trans. Antennas Propag., Vol. 59, No. 7, 2717-2721, July 2011.
5. Singh, H. V., D. V. S. Prasad, S. Tripathi, and A. Mohan, "Closely-coupled wideband MIMO antenna with isolation improvement using decoupling circuit and hexagonal split-ring resonators," Microwave and Optical Technology Letters, Vol. 63, No. 10, 2614-2620, October 2021.
6. Chattha, H. T., "4-port 2-element MIMO antenna for 5G portable applications," IEEE Access, Vol. 7, 96516-96520, June 2019.
7. Liu, D. Q., H. J. Luo, M. Zhang, H. L. Wen, B. Wang, and J. Wang, "An extremely low-profile wideband MIMO antenna for 5G Smartphones," IEEE Trans. Antennas Propag., Vol. 67, No. 9, 5772-5780, September 2019.
8. Wong, K. L., C. M. Chou, Y. J. Yang, and K. Y. Wang, "Multipolarized wideband circular patch antenna for fifth-generation multi-input-multi-output access-point application," IEEE Antennas Wireless Propag. Lett., Vol. 18, No. 10, 2184-2188, October 2019.
9. Ren, Z., A. Zhao, and S. Wu, "MIMO antenna with compact decoupled antenna pairs for 5G mobile terminals," IEEE Antennas Wireless Propag. Lett., Vol. 18, 1367-1371, July 2019.
10. Sun, L., H. Feng, Y. Li, and Z. Zhang, "Compact 5G MIMO mobile phone antennas with tightly arranged orthogonal-mode pairs," IEEE Trans. Antennas Propag., Vol. 66, No. 11, 6364-6369, November 2018.
11. Huang, H., X. Li, and Y. Liu, "5G MIMO antenna based on vector synthetic mechanism," IEEE Antennas Wireless Propag. Lett., Vol. 17, No. 6, 1052-1055, June 2018.
12. Saxena, S., B. K. Kanaujia, S. Dwari, S. Kumar, H. C. Choi, and K. W. Kim, "Planar four-port dual circularly-polarized MIMO antenna for sub-6 GHz band," IEEE Access, Vol. 8, 90779-90791, 2020.
13. Jehangir, S. S. and M. S. Sharawi, "A compact single-layer four-port orthogonally polarized Yagi-like MIMO antenna system," IEEE Trans. Antennas Propag., Vol. 68, No. 8, 6372-6377, August 2020.
14. Xu, Z. and C. Deng, "High-isolated MIMO antenna design based on pattern diversity for 5G mobile terminals," IEEE Antennas Wireless Propag. Lett., Vol. 19, No. 3, 467-471, March 2020.
15. Wong, K. L., J. Z. Chen, and W. Y. Li, "Four-port wideband annular-ring patch antenna generating four decoupled waves for 5G Multi-Input-Multi-Output access points," IEEE Trans. Antennas Propag., Vol. 69, No. 5, 2946-2951, May 2021.
16. Sun, L., Y. Li, Z. Zhang, and Z. Feng, "Wideband 5G MIMO antenna with integrated orthogonal-mode dual-antenna pairs for metal-rimmed smartphones," IEEE Trans. Antennas Propag., Vol. 68, No. 4, 2494-2503, April 2020.
17. Dong, Y., H. Toyao, and T. Itoh, "Design and characterization of miniaturized patch antennas loaded with complementary split-ring resonators," IEEE Trans. Antennas Propag., Vol. 60, No. 2, 772-785, February 2012.
18. Ameen, M., O. Ahmad, and R. K. Chaudhary, "Bandwidth and gain enhancement of triple-band MIMO antenna incorporating metasurface based reflector with for WLAN/WiMAX applications," IET Microwave, Antennas Propag., Vol. 14, No. 13, 1493-1503, October 2020.
19. Abhilash, A. P., K. K. Indhu, R. A. Kumar, K. Neema, and C. Aanandan, "Ultra-wideband quad element MIMO antenna on a flexible substrate for 5G and wearable applications," Progress In Electromagnetics Research C, Vol. 126, 143-155, 2022.
20. Yon, H., M. A. Aris, N. H. Abd Rahman, N. A. M. Nasir, and H. Jumaat, "A design of decoupling structure MIMO antenna for mutual coupling reduction in 5G application," 2019 International Symposium on Antennas and Propagation (ISAP), 1-3, 2019.
21. Milias, C., et al., "Metamaterial-inspired antennas: A review of the state of the art and future design challenges," IEEE Access, Vol. 9, 89846-89865, 2021.
22. Manteghi, M. and Y. Rahmat-Samii, "Multiport characteristics of a wide-band cavity backed annular patch antenna for multipolarization operations," IEEE Trans. Antennas Propag., Vol. 53, 466-474, January 2005.
23. Li, Z., Y. Zhu, H. Yang, G. Peng, and X. Liu, "A dual-band omnidirectional circular polarized antenna using composite right/left-handed transmission line with rectangular slits for unmanned aerial vehicle applications," IEEE Access, Vol. 8, 100586-100595, 2020.
24. Nokia, "5G spectrum bands explained - Low, mid and high band,", https://www.nokia.com/networks/insights/spectrum-bands-5g-world/#:~:text=5G%20mid%2Dband%20spectrum%20provides,GHz%20range%20as%20particularly%20appealing; 2022 [accessed on 10 May 2022].
25. Kumar, A., A. Q. Ansari, B. K. Kanaujia, J. Kishor, and S. Kumar, "An ultra-compact two-port UWB-MIMO antenna with dual band-notched characteristics," AEU - International Journal of Electronics and Communications, Vol. 114, Feb. 2020.
26. Wang, F., S. Li, Q. Zhou, and Y.-B. Gong, "Compact wideband quad-element MIMO antenna with reversed S-shaped walls," Progress In Electromagnetics Research M, Vol. 78, 193-201, 2019.
27. Ban, Y.-L., C. Li, C.-Y.-D. Sim, G. Wu, and K.-L. Wong, "4G/5G multiple antennas for future multi-mode smartphone applications," IEEE Access, Vol. 4, 2981-2988, 2016.