New extremal binary self-dual codes from a Baumert–Hall array

In this work, we introduce new construction methods for self-dual codes using a Baumert–Hall array. We apply the constructions over the alphabets F₂ and F₄+uF₄ and combine them with extension theorems and neighboring constructions. As a result, we construct 46 new extremal binary self-dual codes of length 68, 26 new best known Type II codes of length 72 and 8 new extremal Type II codes of length 80 that lead to new 3−(80,16,665) designs. Among the new codes of length 68 are the examples of codes with the rare γ=5 parameter in W_68,2. All these new codes are tabulated in the paper.