Orthogonal designs II

AbstractOrthogonal designs are a natural generalization of the Baumert-Hall arrays which have been used to construct Hadamard matrices. We continue our investigation of these designs and show that orthogonal designs of type (1,k) and ordern exist for everyk < n whenn = 2t+2⋅3 andn = 2t+2⋅5 (wheret is a positive integer). We also find orthogonal designs that exist in every order 2n and others that exist in every order 4n. Coupled with some results of earlier work, this means that theweighing matrix conjecture ‘For every ordern ≡ 0 (mod 4) there is, for eachk ⩽n, a square {0, 1, − 1} matrixW = W(n, k) satisfyingWWt =kIn’ is resolved in the affirmative for all ordersn = 2t+1⋅3,n = 2t+1⋅5 (t a positive integer).The fact that the matrices we find are skew-symmetric for allk < n whenn ≡ 0 (mod 8) and because of other considerations we pose three other conjectures about weighing matrices having additional structure and resolve these conjectures affirmatively in a few cases.In an appendix we give a table of the known results for orders ⩽ 64.