The paper describes the implementation and performance analysis of the firstfully-operational beam-space MIMO antenna for the spatial multiplexing of twoQPSK streams. The antenna is composed of a planar three-port radiator with twovaractor diodes terminating the passive ports. Pattern reconfiguration is usedto encode the MIMO information onto orthogonal virtual basis patterns in thefar-field. A measurement campaign was conducted to compare the performance ofthe beam-space MIMO system with a conventional 2-by-?2 MIMO system underrealistic propagation conditions. Propagation measurements were conducted forboth systems and the mutual information and symbol error rates were estimatedfrom Monte-Carlo simulations over the measured channel matrices. The resultsshow the beam-space MIMO system and the conventional MIMO system exhibitsimilar finite-constellation capacity and error performance in NLOS scenarioswhen there is sufficient scattering in the channel. In comparison, in LOSchannels, the capacity performance is observed to depend on the relativepolarization of the receiving antennas.
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