A compact printed ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna with embedded structure is proposed. The proposed MIMO antenna consists of two coplanar waveguide-fed (CPW) antenna elements, and the element with smaller size is built in the radiator of the other element. Thus, the compact size, 30 × 22 mm2, is completely determined by the larger one, which makes the MIMO antenna have similar size to the conventional single UWB antennas. The antenna elements are fed perpendicularly to achieve superior isolation. A T-shaped parasitic stub, a pair of C shaped slots, an extended Z-shaped stub and a rectangular slot are employed and each two structures filter the interference for one antenna element. The achieved rejection bands remain relatively stable over the stop-band frequencies and decline rapidly at cut-off frequencies. Thus the proposed MIMO antenna obtains superior filtering performance. The proposed antenna is fabricated and measured. The measured results indicate that two antenna elements can operate in the impedance bandwidth larger than 3.1-10.6 GHz with notched bands of 5-6 GHz, and the mutual coupling is below -15 dB over the entire UWB frequency spectrum. The proposed MIMO antenna is a competitive candidate for UWB MIMO communication systems.
2. Lim, A. W. C. and V. K. N. Lau, "On the fundamental tradeoff of spatial diversity and spatial multiplexing of MIMO links with imperfect CSIT," ISIT 2006, Seattle, USA, July 9–14, 2006. doi:10.1109/TAP.2014.2333066
7. Kang, L., et al., "Compact offset microstrip-fed MIMO antenna for band-notched UWB application," IEEE Antennas Wireless Propag. Lett., Vol. 14, 1754-1757, 2015. doi:10.1109/LAWP.2014.2329496
8. Tang, T.-C. and K.-H. Lin, "An ultrawideband MIMO antenna with dual band-notched function," IEEE Antennas Wireless Propag. Lett., Vol. 13, 1076-1079, 2014. doi:10.1109/TAP.2014.2387871
9. Li, Q., et al., "Miniaturized double-layer EBG structures for broadband mutual coupling reduction between UWB monopoles," IEEE Trans. Antennas Propag., Vol. 63, 1168-1171, 2015.
10. Zhang, S. and G. F. Pedersen, "Mutual coupling reduction for UWB MIMO antennas with a wideband neutralization line," IEEE Antennas Wireless Propag. Lett., Vol. PP, 1-1, 2015. doi:10.1109/TAP.2012.2207049
11. Zhang, S., et al., "Closely-packed UWB MIMO/diversity antenna with different patterns and polarizations for USB dongle applications," IEEE Trans. Antennas Propag., Vol. 60, 4372-4380, 2012.