A key feature of upcoming 4G wireless communication systems is multiple-input-multiple-output (MIMO) technology. To make the best use of MIMO, the antenna correlation between adjacent antennas should be low (< 0.5). In this context, we propose a correlation reduction technique suitable for closely spaced antennas (distance, d < λ/40). This technique reduces mutual coupling between antennas and concurrently uncorrelates antennas' radiation characteristics by inducing the negative group delay at the target frequency. The validity of the technique is demonstrated with a USB dongle MIMO antenna designed for LTE 700 MHz band. Measurement results show that the antenna correlation is reduced more than 40% using the proposed technique.
1. Sampath, H., S. Talwar, J. Tellado, V. Erceg, and A. Paulraj, "A fourth-generation MIMO-OFDM broadband wireless system: Design, performance, and field trial results," IEEE Commun. Mag., Vol. 40, No. 9, 143-149, 2002. doi:10.1109/MCOM.2002.1031841
2. Vaughan, R. G. and J. B. Andersen, "Antenna diversity in mobile communications," IEEE Trans. Veh. Technol., Vol. 26, No. 4, 149-172, Nov. 1987.
3. Carrasco, H., H. D. Hristov, R. Feick, and D. Cofre, "Mutual coupling between planar inverted-F antennas," Microwave Opt. Technol. Lett., Vol. 42, No. 3, 224-227, Aug. 2004. doi:10.1002/mop.20259
4. Karaboikis, M., C. Soras, G. Tsachtsiris, and V. Makios, "Multi element antenna systems for diversity and MIMO terminal devices ," PIERS Proceedings, 2004.
5. Thaysen, J. and K. Jakobsen, "Wireless systems design considerations for low antenna correlation and mutual coupling reduction in multi antenna terminals," Eur. Trans. Telecommun., Vol. 18, No. 3, 319-326, Apr. 2006. doi:10.1002/ett.1111
6. 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. doi:10.1109/TAP.2003.817983
7. Nashaat Elsheakh, D. N., M. F. Iskander, E. A.-F. Abdallah, H. A. Elsadek, and H. Elhenawy, "Microstrip array antenna with new 2D-electromagnetic band gap structure shapes to reduce harmonics and mutual coupling," Progress In Electromagnetics Research C, Vol. 12, 203-213, 2010. doi:10.2528/PIERC09112008
8. Chung, Y., S. S. Jeon, D. Ahn, J. I. Choi, and T. Itoh, "High isolation dual-polarized patch antenna using defected ground structure," IEEE Microw. Wireless Compon. Lett., Vol. 14, No. 1, 4-6, 2004. doi:10.1109/LMWC.2003.821501
9. Chiu, C.-Y., C.-H. Cheng, R. D. Murch, and C. R. Rowell, "Reduction of mutual coupling between closely-packed antenna elements ," IEEE Trans. Antennas Propag., Vol. 55, No. 6, 1732-1738, Jun. 2007. doi:10.1109/TAP.2007.898618
10. Chen, S.-C., Y.-S. Wang, and S.-J. Chung, "A decoupling technique for increasing the port isolation between two strongly coupled antennas," IEEE Trans. Antennas Propag., Vol. 56, No. 12, 3650-3658, Dec. 2008. doi:10.1109/TAP.2008.2005469
11. Bhatti, R. A., S. Yi, and S. Park, "Compact antenna array with port decoupling for LTE-standardized mobile phones," IEEE Antennas Wireless Propag. Lett., Vol. 8, 430-1433, 2009.
12. Mak, A. C. K., C. R. Rowell, and R. D. Murch, "Isolation enhancement between two closely packed antennas," IEEE Trans. Antennas Propag., Vol. 56, No. 11, 3411-3419, Nov. 2008. doi:10.1109/TAP.2008.2005460
13. Li, C., S. Chen, and P. Hsu, "Integrated dual planar inverted-F antenna with enhanced isolation," IEEE Antennas Wireless Propag. Lett., Vol. 8, 963-965, 2009.
14. Diallo, A., C. Luxey, P. L. Thuc, R. Staraj, and G. Kossiavas, "Study and reduction of the mutual coupling between two mobile phone PIFAs operating in the DCS1800 and UMTS bands," IEEE Trans. Antennas Propag., Vol. 54, No. 11, 3063-3074, Nov. 2006. doi:10.1109/TAP.2006.883981
15. Chiu, C.-W., C.-H. Chang, and Y.-J. Chi, "A meandered loop antenna for LTE/WWAN operations in a smart phone," Progress In Electromagnetics Research C, Vol. 16, 147-160, 2010. doi:10.2528/PIERC10072503
16. Bolda, E. L., R. Y. Chiao, and J. C. Garrison, "Two theorems for the group velocity in dispersive media," Phys. Rev. A, Vol. 48, No. 5, 3890-3894, 1993. doi:10.1103/PhysRevA.48.3890
17. Siddiqui, O. F., M. Mojahedi, and G. V. Eleftheriades, "Periodically loaded transmission line with effective negative refractive index and negative goup delay," IEEE Trans. Antennas Propag., Vol. 51, No. 10, 2619-2625, 2003. doi:10.1109/TAP.2003.817556
18. Withayachumnankul, W., B. M. Fischer, B. Ferguson, B. R. Davis, and D. Abbott, "A systemized view of superluminal wave propagation," Proc. IEEE, Vol. 98, No. 10, 1775-1786, Oct. 2010. doi:10.1109/JPROC.2010.2052910
19. Stenlus, P. and B. York, "On the propagation of transients in waveguides," IEEE Antennas and Propag. Mag., Vol. 37, No. 2, 39-44, Apr. 1995. doi:10.1109/74.382337
21. Siddiqui, O. F., S. J. Erickson, G. V. Eleftheriades, and M. Mojahedi, "Time domain measurement of negative group delay in negative refractive index transmission line metamaterials," IEEE Trans. Microw. Theory Tech., Vol. 52, No. 5, 1449-1454, May 2004. doi:10.1109/TMTT.2004.827018
22. Ravelo, B., A. Perennec, M. Le Roy, and Y. Boucher, "Active microwave circuit with negative group delay," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 12, 861-863, Dec. 2007. doi:10.1109/LMWC.2007.910489
23. Choi, H., Y. Jeong, C. D. Kim, and J. S. Kenney, "Efficiency enhancement of feedforward amplifiers by employing a negative group-delay circuit," IEEE Trans. Microw. Theory Tech., Vol. 58, No. 5, 1116-1125, May 2010. doi:10.1109/TMTT.2010.2045576
24. Kildal, P. S. and K. Rosengren, "Correlation and capacity of MIMO systems and mutual coupling, radiation efficiency, and diversity gain of their antennas: Simulations and measurements in a reverberation chamber," IEEE Commun. Mag., Vol. 42, 104-112, 2004. doi:10.1109/MCOM.2004.1367562