The design of dual-frequency band Inverted-S Antennas (ISA) involves a great deal of tuning works. In this point of view, two optimal methodologies are proposed to synthesis this type of antennas in a more efficient way. The two optimal methodologies, one based on a vector optimizer and the other on scalar optimizer, take advantage of a novel formula to optimize the bandwidths in dual bands. The scalar methodology employs some constraint handling technique to improve its speed of convergence, while the vector methodology without using any preference information strives to accelerate its convergence by means of response surface models. The comparison of numerical results shows the feasibility of the proposed optimal methodology for ISA synthesis. Also, the advantages and limitations of the methodologies are discussed.