A compact UWB (Ultrawideband) MIMO (Multiple-input multiple-output) antenna with asymmetric coplanar strip (ACS)-fed structure is proposed in this paper. The antenna consists of two modified ACS feeding staircase-shaped radiation elements which are orthogonally placed, and the wideband isolation is achieved through a fence-like stub between them. The effectiveness of the fence-like stub is analyzed. Measured results show that the presented antenna can achieve a broad impedance bandwidth (|S11|≤-10 dB) of 3.1-11 GHz with good performance in terms of isolation >15 dB. Radiation patterns and correlation coefficient (ECC) denote the consistent diversity performance across the entire UWB bandwidth. By introducing the ACS-fed structure, the antenna size can be considerably reduced to 43.5 mm×43.5 mm×1.6 mm compared to the recently published UWB MIMO antennas, which makes the antenna suitable for portable UWB MIMO applications.
2. Dietrich, C. B., K. Dietze, J. R. Nealy, and W. L. Stutzman, "Spatial, polarization, and pattern diversity for wireless handheld terminals," IEEE Trans. on Antennas and Propagat., Vol. 49, No. 9, 1271-1281, Sep. 2001.
3. Wei, K. P., Z. J. Zhang, W. H. Chen, and Z. H. Feng, "A novel hybrid-fed patch antenna with pattern diversity," IEEE Antennas Wireless Propag. Lett., Vol. 9, 562-565, Apr. 2010.
4. Chacko, B. P., G. Augustin, and T. A. Denidni, "Uniplanar slot antenna for ultrawideband polarization-diversity applications," IEEE Antennas Wireless Propag. Lett., Vol. 12, 88-91, Jan. 2013.
5. Najam, A., Y. Duroc, and S. Tedjni, "UWB-MIMO antenna with novel stub structure," Progress In Electromagnetics Research Letters, Vol. 19, 245-257, 2011.
6. Liu, X.-L., Z.-D. Wang, Y.-Z. Yin, and J.-H. Wang, "Closely spaced dual band-notched UWB antenna for MIMO applications," Progress In Electromagnetics Research Letters, Vol. 46, 109-116, 2014.
7. Gao, P., S. He, X. B. Wei, N. Wang, and Y. Zheng, "Compact printed UWB diversity slot antenna with 5.5 GHz band-notched characteristics," IEEE Antennas Wireless Propag. Lett., Vol. 13, 376-379, Feb. 2014.
8. Antonino-Daviu, E., M. Gallo, B. Bernardo-Clemente, and M. Ferrando-Bataller, "Ultrawideband slot ring antenna for diversity applications," Electron. Lett., Vol. 46, No. 7, 478-480, Apr. 2010.
9. Gallo, M., E. Antonono-Daviu, M. Ferrando-Bataller, M. Bozzetti, J. Molina-Garcia-Pardo, and L. Juan-Llacer, "A broadband pattern diversity annular slot antenna," IEEE Trans. on Antennas and Propagat., Vol. 60, No. 3, 1596-1600, May 2012.
10. Hong, S., K. Chung, J. Lee, and S. Jung, "Design of a diversity antenna with stubs for UWB applications," Microwave Opt. Technol. Lett., Vol. 50, 1352-1356, 2008.
11. Lee, J. M., K. B. Kim, H. K. Ryu, and J. M. Woo, "A compact ultrawideband MIMO antenna with WLAN band-rejected operation for mobile devices," IEEE Antennas Wireless Propag. Lett., Vol. 11, 990-993, Aug. 2012.
12. Li, Y. S., W. X. Li, and Q. B. Ye, "Miniaturation of asymmetric coplanar strip-fed staircase ultrawideband antenna with reconfigurable notch band," Microwave Opt. Technol. Lett., Vol. 55, 1467-1470, 2013.
13. Fei, P., Y. C. Jiao, Y. Zhu, and F. S. Zhang, "Compact CPW-fed monopole antenna and miniaturized ACS-fed half monopole antenna for UWB applications," Microwave Opt. Technol. Lett., Vol. 54, 1605-1609, 2012.
14. Lotfi, P., M. Azarmanesh, and S. Soltani, "Retatable dual band-notched UWB-triple-band WLAN reconfigurable antenna," IEEE Antennas Wireless Propag. Lett., Vol. 12, 388-391, Apr. 2013.
15. Li, X., X. W. Shi, W. Hu, P. Fei, and J. F. Yu, "Compact triband ACS-fed monopole antenna employing open-ended slots for wireless communication," IEEE Antennas Wireless Propag. Lett., Vol. 12, 104-107, Apr. 2013.
16. Fang, S. J. and B. S. Wang, "Analysis of asymmetric coplanar waveguide with conductor backing," IEEE Transactions on Microwave Theory and Techniques, Vol. 47, No. 2, 238-240, Feb. 1999.
17. Vaughan, R. G. and J. B. Anderson, "Antenna diversity in mobile communications," IEEE Trans. Vehicular Technology, Vol. 36, No. 4, 149-171, 1987.
18. Blanch, S., J. Romeu, and I. Corbella, "Exact representation of antenna system diversit performance from input parameter description," Electron. Lett., Vol. 39, No. 9, 705-707, May 2003.