improvements are, respectively, noticed according to the SISO case. However, compared to the results shown in Figure 9, higher BER levels are obtained, in this case, for the same SNR. This is due to the high delay spreading of the isotropic channel. The generated WiMAX frame is transmitted with respect to a certain power level. This level is changed by a 2 dBm step during the evaluation process. The system performances are then quantified by computing the mean BER levels at each step. The obtained results show the improvements provided by the use of multiple antennas techniques (cf. Fig. 12). For a high transmit- ting power, the BER level do not reach 10 2 in the SISO case, while it moves closer to 10 3 in the MISO and MIMO cases. Likewise, to ensure a BER of 10 2 , the SISO system needs to transmit data with a power level of nearly 15 dBm, while the MISO system needs only 30 dBm. This represents a 15 dB power saving between the two configurations. Moreover, this power saving level can be enhanced up to 20 dB with the use of MIMO. These statements can be, clearly, observed in Figure 13, where the BER gain relative to each couple of antenna configu- rations is illustrated over the considered power range. 5. CONCLUSIONS Performances of a WiMAX MIMO-OFDM system have been studied through active measurements in a reverberation chamber. The aim of these tests is to estimate the contribution of MIMO techniques on this system in such a controlled environment. Moreover, this kind of tests allows evaluating and comparing per- formances of real systems in a reference context. Such an experi- mental system is influenced by many hardware or measurement context imperfections. For this reason, some corrections techni- ques have been set up and presented in this article. Improvements due to the use of multi-antennas and numerical correction techni- ques have been shown through the obtained results. The follow- ing step is to emulate channels with known PDP and AOA. This could help for conducting different kind of experiments: • Evaluation and comparison of different MIMO systems performances in a reference channel. • Evaluation and comparison of different estimation and cor- rection algorithms performances in such channels. • Evaluation of the antennas parameters (coupling, antenna efficiency, etc.) on the real system capacities. Figure 13 BER gain between the used antenna configurations REFERENCES 1. WiMax Forum-Technology, Available at: http://www.wimaxforum.org. 2. IEEE, IEEE standard for local and metropolitan area networks, Part 16, IEEE 802. 16–2004, New York, NY, 2004. 3. IEEE, IEEE standard for local and metropolitan area networks, Part 16, IEEE 802.16e-2005, New York, NY, 2005. 4. K. Rosengren and P-S. Kildal, Study of distributions of modes and plane waves in reverberation chambers for the characterization of antennas in a multipath environment, Microwave Opt Technol Lett 30 (2001). 5. C. Tounou, C. Decroze, D. Carsenat, T. Monediere, and B. Jecko, Diversity antennas efficiencies enhancement, In: Proceedings of IEEE Antennas and Propagation International Symposium, Honolulu, HI, 2007, pp. 1064–1067. 6. A. Diallo, C. Luxey, P.L. Thuc, R. Staraj, and G. Kossiavas, Di- versity performance of multiantenna systems for UMTS cellular phones in different propagation environments, In: Proceedings of The European Conference on Antennas and Propagation: EuCAP 2006, Vol. 2008, 2008. 7. J.F. Valenzuela-Valdes, M.A. Garcia-Fernandez, A.M. Martinez- Gonzalez, and D.A. Sanchez-Hernandez, The influence of effi- ciency on receive diversity and MIMO capacity for rayleigh-fading channels, IEEE Trans Antennas Propag 56 (2008), 1444–1450. 8. J.F. Valenzuela-Valde ´s, et al., Diversity gain and MIMO capacity for non-isotropic environments using a reverberation chamber, IEEE Antennas Wireless Propag Lett, in press. 9. C. Decroze, D. Carsenat, M. Mouhamadou, C. Tounou, S. Rey- naud, and T. Mone ´die `re, Measurement of antenna diversity per- formances on a compact wireless device in real environment, Presented at the IEEE International Symposium on Antennas and propagation, San Diego, 2008. 10. M.B. Knudsen and G.F. Pedersen, Spherical outdoor to indoor power spectrum model at the mobile terminal, 20 (2002), 1156– 1169. 11. S.M. Alamouti, A simple transmit diversity technique for wireless communications, IEEE J Select Areas Commun 16 (1998). 12. S. Coleri, M. Ergen, A. Puri, and A. Bahai, Channel estimation techniques based on pilot arrangement in OFDM systems, IEEE Trans Broadcast 48 (2002). 13. A. Pascual, L.M. Ventura, and X. Nieto, Residual carrier frequency offsetestimation and correction in OFDM MIMO systems, Pre- sented at the IEEE International Symposium on Personal, Indoor, and Mobile Radio Communications, September 2007. 14. O.A. Alim, N. Elboghdadly, M. Ashour, and A. Elaskary, Channel estimation and equalization for fixed/mobile OFDM WiMAX sys- tem in simulink, Mobilware’08, Austria, 2008. V C 2010 Wiley Periodicals, Inc. EFFICIENT AND HIGH-GAIN APERTURE COUPLED SUPERSTRATE ANTENNA ARRAYS FOR 60 GHz INDOOR COMMUNICATION SYSTEMS Hamsakutty Vettikalladi, Laurent Le Coq, Olivier Lafond, and Mohamed Himdi Institute of Electronics and Telecommunication of Rennes (IETR), University of Rennes1, Rennes Cedex 35042, France; Corresponding author: hamsakutty.vettikalladi@univ-rennes1.fr Received 8 January 2010 ABSTRACT: Efficient and high-gain aperture coupled patch antenna arrays with superstrate at 60 GHz are studied and presented. It is noted that adding a superstrate with a specific size will induce a significant effect on antenna gain and radiation patterns. This capability is applied on the design of 2  2 and 4  4 arrays for high-gain application. The maximum measured gain of a 2  2 superstrate antenna array is 16 dBi 2352 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 10, October 2010 DOI 10.1002/mop