This paper presents a new design approach for compact orthogonal broadband printed multiple-input multiple-output (MIMO) antennas based on a coplanar waveguide (CPW)-fed hexagonal-ring monopole antenna (HRMA) element. The design procedure of the basic radiating element is initiated from a stripline (SL)-fed circular monopole antenna (CMA). Then various antennas involved in the design evolution process are introduced to attain a compact CPW-fed HRMA. This basic antenna element has a compact size of 13×10 mm2, 50% smaller than SL-fed CMA, and a prototype of this antenna is built and tested. Based on HRMA element, compact two- and four-element MIMO antenna systems are designed, fabricated and experimentally demonstrated for 5-GHz ISM band operation. The MIMO antenna systems use orthogonally configured of identical closely spaced HRMA elements, with CPW-fed printed on one side of the substrate to achieve good isolation. Design simulation is carried out with the aid of Computer Simulation Technology Microwave Studio (CST MWS) and confirmed with High Frequency Structure Simulator (HFSS). The experimental results are in close agreement with the simulated ones, which validates the design principle. Based on experimental results, the two MIMO antenna systems have an impedance bandwidth of more than 2 GHz, good isolation of less than 15 dB, and a low envelope correlation coefficient of better than -26 dB across the frequency band of (4-6 GHz), which are suitable for 5-GHz MIMO applications.
2. Malik, J., A. Patnaik, and M. V. Kartikeyan, "Novel printed MIMO antenna with pattern and polarization diversity," IEEE Antennas Wireless Propag. Lett., Vol. 14, 739-742, 2015.
3. Akdagli, A. and A. Toktas, "Design of wideband orthogonal MIMO antenna with improved correlation using a parasitic element for mobile handsets," International Journal of Microwave and Wireless Technologies, Vol. 7, 1-7, 2014.
4. Marzudi, W. N. N. W., Z. Z. Abidin, S. H. Dahlan, M. Yue, R. A. Abd-Alhameed, and M. B. Child, "A compact orthogonal wideband printed MIMO antenna for WiFi/WLAN/LTE applications," Microwave Opt. Technol. Lett., Vol. 57, No. 7, 1733-1738, Jul. 2015.
5. See, C. H., R. A. Abd-Alhameed, N. J. McEwan, S. M. R. Jones, R. Asif, and P. S. Excell, "Design of a printed MIMO/diversity monopole antenna for future generation handheld devices," International Journal of RF and Microwave Computer-Aided Engineering, Vol. 24, No. 3, 348-359, May 2014.
6. Babu, K. J., R. W. Aldhaheri, M. Y. Talha, and I. S. Alruhaili, "Design of a compact two element MIMO antenna system with improved isolation," Progress In Electromagnetics Research Letters, Vol. 48, 27-32, 2014.
7. Li, Z., Z. Du, M. Takahashi, K. Saito, and K. Ito, "Reducing mutual coupling of MIMO antennas with parasitic elements for mobile terminals," IEEE Trans. Antennas Propag., Vol. 60, No. 2, 473-481, Feb. 2012.
8. Li, J.-F., Q.-X. Chu, and T.-G. Huang, "A compact wideband MIMO antenna with two novel bent slits," IEEE Trans. Antennas Propag., Vol. 60, No. 2, 482-489, Feb. 2012.
9. Su, S.-W., C.-T. Lee, and F.-S. Chang, "Printed MIMO-antenna system using neutralization-line technique for wireless USB-dongle applications," IEEE Trans. Antennas Propag., Vol. 60, No. 2, 456-463, Feb. 2012.
10. Wang, Y. and Z. Du, "A wideband printed dual-antenna with three neutralization lines for mobile terminals," IEEE Trans. Antennas Propag., Vol. 62, No. 3, 1495-1500, Mar. 2014.
11. Zhao, L. and K.-L. Wu, "A dual-band coupled resonator decoupling network for two coupled antenna," IEEE Trans. Antennas Propag., Vol. 63, No. 7, 2843-2850, Jul. 2015.
12. Zhang, Z., H. Wang, and Z. Feng, "Dual-port planar MIMO antenna with ultra-high isolation and orthogonal radiation patterns," Electronics Letters, Vol. 51, No. 1, 7-8, Jan. 2015.
13. Mallahzadeh, A. R., S. Es'haghi, and A. Alipour, "Design of an E-shaped MIMO antenna using IWO algorithm for wireless application at 5.8 GHz," Progress In Electromagnetics Research, Vol. 90, 187-203, 2009.
14. Ryan, C. G. M. and G. V. Eleftheriades, "Two compact, wideband, and decoupled meanderlin antennas based on metamateria concepts," IEEE Antennas Wireless Propag. Lett., Vol. 11, 1277-1280, 2012.
15. Zhang, X.-Y., X. Zhong, B. Li, and Y. Yu, "A dual-polarized MIMO antenna with EBG for 5.8 GHz WLAN application," Progress In Electromagnetics Research Letters, Vol. 51, 15-20, 2015.
16. Wang, K., R. A. M. Mauermayer, and T. F. Eibert, "Compact two-element printed monopole array with partially extended ground plane," IEEE Antennas Wireless Propag. Lett., Vol. 13, 138-140, 2014.
17. Poole, I., "IEEE 802.11ac Gigabit Wi-Fi,", 2013 [Online], Avaible: http://www.radio-electronics.com/info/wireless/wi-fi/ieee-802-11acgigabit.php.
18. Sharawi, M. S., M. U. Khan, A. B. Numan, and D. N. Aloi, "A CSRR loaded MIMO antenna system for ISM band operation," IEEE Trans. Antennas Propag., Vol. 61, No. 8, 4265-4274, Aug. 2013.
19. Ghosh, S., T.-N. Tran, and T. L.-Ngoc, "Dual-layer EBG-based miniaturized multi-element antenna for MIMO systems," IEEE Trans. Antennas Propag., Vol. 62, No. 8, 3985-3997, Aug. 2014.
20. Dai, X.-W., L. Li, Z.-Y.Wang, and C-H. Liang, "High isolation and compact MIMO antenna system with defected shorting wall," International Journal of Microwave and Wireless Technologies, Vol. 7, 1-6, 2014.
21. Abdalla, M. A. and A. A. Ibrahim, "Compact and closely spaced metamaterial MIMO antenna with high isolation for wireless applications," IEEE Antennas Wireless Propag. Lett., Vol. 12, 1452-1455, 2013.
22. Kushwaha, N. and R. Kumar, "Design of slotted ground hexagonal microstrip patch antenna and gain improvement with FSS screen," Progress In Electromagnetics Research B, Vol. 51, 177-199, 2013.
23. Karimian, R., H. Oraizi, S. Fakhte, and M. Farahani, "Novel F-shaped quad-band printed slot antenna for WLAN and WiMAX MIMO systems," IEEE Antennas Wireless Propag. Lett., Vol. 12, 405-408, 2013.
24. Moon, J. and Y. Kim, "Antenna diversity strengthens wireless LANs," Communication Systems Design, 15-22, Jan. 2003.
25. Kulkarni, A. and S. K. Sharma, "A multiband antenna with MIMO implementation for USB dongle size wireless devices," Microw. Opt. Technol. Lett., Vol. 54, No. 8, 1990-1994, Aug. 2012.
26. Blanch, S., J. Romeu, and I. Corbella, "Exact representation of antenna system diversity performance from input parameter description," Electronics Letters, Vol. 39, No. 9, 705-707, May 2003.
27. Fakhr, R. S., A. A. Lotfi-Neyestanak, and M. Naser-Moghadasi, "Compact size and dual band semicircle shaped antenna for MIMO applications," Progress In Electromagnetics Research C, Vol. 11, 147-154, 2009.
28. Luo, Y., Q.-X. Chu, J.-F. Li, and Y.-T. Wu, "A planar H-shaped directive antenna and its application in compact MIMO antenna," IEEE Trans. Antennas Propag., Vol. 63, No. 9, 4810-4814, 2013.
29. Moghadasi, M. N., A. Danideh, A. Bakhtiari, and R. Sadeghifakhr, "Compact slot antenna for MIMO applications in the WLAN bands," Microwave Opt. Technol. Lett., Vol. 55, No. 10, 2490-2493, Oct. 2013.