As a type of space-filling designs,uniform designs are widely applied in various fields because of flexibility of runs and model robustness.The method of doubling plays an important role in construction of optimal two-level designs.In this paper,the construction of doubling for two-level designs is extended to four-level and mixed two- and four-level designs,the new conception on four-level and mixed two- and four-level Double designs are presented.Under the wrap-around ${L_2}$-discrepancy,the relationships of uniformity between such Double designs and their initial designs are investigated.Mo...