There is provided mechanisms for configuring an antenna system having individual antenna elements arranged in at least two antenna subarrays. Each pair of antenna subarrays has a respective first spatial separation. Each pair of the individual antenna elements has a respective second spatial separation. A method is performed by a network device. The method includes obtaining channel measurements for each of the at least two antenna subarrays. Channel covariance information between the subarrays using the obtained channel measurements is determined. Channel covariance information between all individual antenna elements of the antenna system is determined by interpolating the channel covariance information between the subarrays according to a spatial relation between all first spatial separations and all second spatial separations. Combining of the individual antenna elements of the antenna system is controlled based on the determined channel covariance information between all the individual antenna elements.