Certain aspects involve a spatial separation sub-system for a distributed antenna system ("DAS"). The spatial separation sub-system can include input ports that are communicatively connectable to a base station, output ports that are communicatively connectable to remote antenna units of the DAS, and RF circuitry that communicatively connects the input ports and the output ports. The spatial separation sub-system can receive at least two downlink signals via at least two of the input ports. A phase difference between the downlink signals can correspond to a codebook index used to encode the downlink signals for multiple-input/multiple-output ("MIMO") transmission. The RF circuitry can provide a combined signal power from the downlink signals to one of the output ports based on the phase difference between the downlink signals.
