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In this paper, we present a theoretical analysis on the gains offered by a reconfigurable Multiple-Input MultipleOutput (MIMO) system using Orthogonal Space-Time Block Codes (OSTBCs) and reconfigurable antennas at the receiver only. The proposed system using reconfigurable antennas selects the optimal radiation state of the receive antennas in which the receive Signal-to-Noise Ratio (SNR) is maximized. The theoretical findings show that under certain channel propagation conditions and using an appropriate codification and power allocation of the transmitted signal, the diversity order of the proposed reconfigurable MIMO system is given by the product of transmit and receive antennas as well as the number of reconfigurable radiation states of the receive antennas. The impact of correlated radiation states and imperfect channel estimation are also considered. The geometrical and physical constrains of reconfigurable antennas are also taken into account through the concept of antenna group. Assuming an ideally scattered NonLine-of-Sight (NLOS) flat Rayleigh channel, the antenna design criteria is given. Finally, we evaluate the theoretical findings through simulations on the array gain, bit error rate and ergodic capacity, where the detrimental impact of channel estimation is observed.

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Abstract-This paper presents the theory, design procedure, and implementation of a dual-band planar quadrature hybrid with enhanced bandwidth. The topology of the circuit is a three-branch-line (3-BL) quadrature hybrid, which provides much larger flexibility to allocate the desired operating frequencies and necessary bandwidths than other previously published configurations. A performance comparison with other dual-band planar topologies is presented. Finally, a 3-BL quadrature hybrid for dual band (2.4 and 5 GHz) wireless local area network systems was fabricated, aimed to cover the bands corresponding to the standards IEEE802.11a/b. The measurements show a 16% and 18% bandwidth for the lower and upper frequency, respectively, satisfying and exceeding the bandwidth requirements for the above standards.Index Terms-Dual-band hybrid, planar quadrature hybrid, wireless local area network (WLAN) systems.

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