We report a measurement of the diffractive structure function FDjj of the antiproton obtained from a study of dijet events produced in association with a leading antiproton in p¯p collisions at s√=630GeV at the Fermilab Tevatron. The ratio of FDjj at s√=630GeV to FDjj obtained from a similar measurement at s√=1800GeV is compared with expectations from QCD factorization and other theoretical predictions. We also report a measurement of the ξ ( x-Pomeron) and β ( x of parton in Pomeron) dependence of FDjj at s√=1800GeV. In the region 0.035<ξ<0.095, |t|<1GeV2, and β<0.5, FDjj(β,ξ) is found to be of the form β−1.0±0.1ξ−0.9±0.1, which obeys β-ξ factorization.