Classical mixed partitions

Through a method given in Hirschfeld and Thas (General Galois Geometries, Oxford University Press, Oxford, 1991), a mixed partition of PG(2n−1,q2) can be used to construct a (2n−1)-spread of PG(4n−1,q) and, hence, a translation plane of order q2n. A mixed partition in this case is a partition of the points of PG(2n−1,q2) into PG(n−1,q2)ʹs and PG(2n−1,q)ʹs which we call Baer subspaces. In this paper, we completely classify the mixed partitions which generate regular spreads and, hence, can be classified as classical.