New single-/dual-mode design formulas of the rectangular dielectric resonator antennas (DRAs) are obtained using the covariance matrix adaptation evolutionary strategy (CMA-ES). The new dual-mode formula has an advantage over the previous one in that it allows an input of a specified dimension ratio of the DRA. Also, it is simpler but more accurate than the previous one. To validate our formulas, four dual-band rectangular DRAs of different dimension ratios were designed and fabricated, and the measured resonance frequencies agree very well with the design frequencies. The reflection coefficients, radiation patterns, and antenna gains of one of the dual-band DRAs were also simulated and measured. © 2011 IEEE.