Impact of transmit antenna spacing on 2x1 Alamouti radio transmission

It is a common belief that multiple transmit antennas have to be placed far apart in order to avoid undesired effects such as mutual coupling, changing beampatterns, antenna mismatching losses, and correlation. The following radio communication setup is considered: two lambda/4-monopole ground-plane transmit antennas, a single receive antenna, 4QAM modulation, Alamouti space-time coding, uncoded single carrier transmission at 2.4 GHz, indoor scenario. By measurements, the impact of very low transmit antenna spacing on the average uncoded BER over transmit-power performance of such a radio link, therefore accounting for all losses in the transmission chain, is examined. The common belief that multiple transmit antennas have to be placed far apart cannot be confirmed