A transmitting radio node (10) precodes a transmission from a one-dimensional antenna array (12) to a receiving radio node (50). The array (12) includes co-polarized antenna elements (14) aligned in the array's only spatial dimension. The transmitting radio node (10) precodes the transmission from each of different subarrays (34a, 34b) of the antenna elements (14) using a coarse-granularity precoder that is factorizable from a multi-granular precoder targeting the given spatial dimension of the array (12) at different granularities, so as to virtualize the subarrays (34a, 34b) as different auxiliary elements (38a, 38b). The transmitting radio node (10) also precode the transmission from the different auxiliary elements (38a, 38b) using one or more finer-granularity precoders that are also factorizable from the multi-granular precoder. In this case, the coarse granularity precoders and the one or more finer-granularity precoders are represented within one or more codebooks (26) used for said precoding.