Abstract. Mobile network operators demand small base station antennas and high physical layer throughputs. In the downlink, high physical layer throughputs can be achieved by exploiting transmit diversity in a MIMO link. As correlation between the different propagation paths reduces the achievable throughput, one is advised to place the transmit antennas "far" apart. Indeed, it is commonly conjectured that the greater the transmit antenna spacing, the better the radio link performance. Although this phenomenon is well understood in quality, the open question remains for exact quantitative behavior, that is, how much does the throughput of a communication system actually change over antenna spacing? In this paper, we answer this question by closed-loop throughput measurements at 2.5 GHz for standard compliant 2