Abstract: Wireless communication apparatus (20) includes a transmitter (22), which includes a first plurality of transmit antennas (26) mutually separated by a first spacing, and which is configured to transmit signals via the transmit antennas over multiple spatial sub-channels, the signals having respective phases. A receiver (24), which includes a second plurality of receive antennas (28) mutually separated by a second spacing, is configured to receive the signals over the multiple spatial sub-channels via the receive antennas. The first and second spacings are chosen so as to maximize a linear independence of the respective phases of the signals received at the receive antennas.