In this paper, a second-order decoupling design using a resonator and an interdigital capacitor is proposed for an MIMO antenna pair in mobile terminals. The proposed antenna pair consists of an interdigital capacitor and an open loop resonator. By properly combining the responses of the resonator and interdigital capacitor, a second-order decoupling performance can be achieved. Meanwhile, isolation between the two antennas is increased by at least 15 dB within the frequency band of interest, from -5 dB to -20 dB. Moreover, the decoupled antenna pair maintains good impedance matching performance from 2.4 GHz to 2.5 GHz. The proposed decoupled antenna pair and its coupled counterpart have been fabricated and measured. The measured results agree with the simulation ones. The proposed MIMO antenna pair is an eligible candidate for Wi-Fi MIMO applications in the 2.4 GHz band.
2. Lee, C. H., S. Y. Chen, and P. W. Hsu, "Integrated dual planar inverted-F antenna with enhanced isolation," IEEE Antennas Wireless Propag. Lett., Vol. 8, 963-965, 2009.
3. 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, 2014.
4. See, C. H., R. A. Abd-Alhameed, Z. Z. Abidin, N. J. McEwan, and P. S. Excell, "Wideband printed MIMO/diversity monopole antenna for WiFi/WiMAX applications," IEEE Trans. Antennas Propag., Vol. 60, No. 4, 2028-2035, Apr. 2012.
5. 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.
6. Lai, X. Z., Z. M. Xie, X. L. Cen, and Z. Y. Zheng, "A novel technique for broadband circular polarized PIFA and diversity PIFA systems," Progress In Electromagnetics Research, Vol. 142, 41-55, 2013.
7. Zuo, S., Y.-Z. Yin, Y. Zhang, W.-J. Wu, and J.-J. Xie, "Eigenmode decoupling for MIMO loopantenna based on 180 coupler," Progress In Electromagnetics Research Letter, Vol. 26, 11-20, 2011.
8. Yeung, L. K. and Y. E.Wang, "Mode-based beamforming arrays for miniaturized platforms," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 1, 45-52, Jan. 2009.
9. Coetzee, J. C. and Y. Yu, "Port decoupling for small arrays by means of an eigenmode feed network," IEEE Trans. Antennas Propag., Vol. 56, No. 6, 1587-1593, Jun. 2008.
10. Yang, F. and Y. Rahmat-Samii, "Microstrip antennas integrated with Electromagnetic Band-Gap (EBG) structures: A low mutual coupling design for array applications," IEEE Trans. Antennas Propag., Vol. 51, No. 10, 2936-2946, Oct. 2003.
11. Li, Q., et al., "Miniaturized double-layer EBG structures for broadband mutual coupling reduction between UWB monopoles," IEEE Trans. Antennas Propag., Vol. 63, No. 3, 1168-1171, 2015.
12. Li, L., B. Li, H. X. Liu, and C. H. Liang, "Locally resonant cavity cell model for electromagnetic band gap structures," IEEE Trans. Antennas Propag., Vol. 54, No. 1, 90-100, Jan. 2006.
13. Suwailam, M., M. Boybay, and O. Ramahi, "Electromagnetic coupling reduction in high-profile monopole antennas using single-negative magnetic metamaterials for MIMO applications," IEEE Trans. Antennas Propag., Vol. 58, No. 9, 2894-2902, Sep. 2010.
14. Habashi, A., J. Nourinia, and C. Gobadi, "Mutual coupling reduction between very closely spaced patch antennas using low-profile Folded Split-Ring Resonators (FSRRs)," IEEE Antennas and Wireless Propagation Letters, Vol. 10, 2011.
15. Qian, K.-W., L. Zhao, and K.-L. Wu, "An LTCC coupled resonator decoupling network for two antennas," IEEE Trans. Antennas Propag., Vol. 63, No. 10, 3199-3207, Oct. 2015.
16. Zhao, L., K.-W. Qian, and K.-L. Wu, "A cascaded coupled resonator decoupling network for mitigating interference between two radios in adjacent frequency bands," IEEE Trans. Microw. Theory Techn., Vol. 62, No. 11, 2680-2688, Nov. 2014.
17. Zhao, L. and K.-L. Wu, "A decoupling technique for four-element symmetric arrays with reactively loaded dummy elements," IEEE Trans. Antennas Propag., Vol. 62, No. 8, 4416-4421, Aug. 2014.
18. Yeung, L. K. and K.-L. Wu, "A compact second-order LTCC band-pass filter with two finite transmission zeros," IEEE Trans. Microw. Theory Techn., Vol. 51, No. 2, 337-341, 2003.
19. Zhao, L., L. K. Yeung, and K.-L. Wu, "A coupled resonator decoupling network for two-element compact antenna arrays in mobile terminals," IEEE Trans. Antennas Propag., Vol. 62, No. 5, 2767-2776, May 2014.
20. Zhao, L. and K.-L. Wu, "A broadband coupled resonator decoupling network for a three-element compact array," IEEE MTT-S Int. Microw. Symp. Dig., Jun. 2013.