A systematic design approach using the developed numerical model for the investigation of any arbitrary electrooptic modulator configuration is described, and its application to the simulation and synthesis of resonantly enhanced Mach-Zehnder modulators (RE-MZMs) is demonstrated. The tool is implemented using equivalent circuit model using transmission lines, lumped elements, and N-port S-parameters. The numerical tool is used to simulate the modulation enhancement factor and radio frequency (RF) return loss of a number of theoretically and experimentally demonstrated examples. Finally, the design tool is used to synthesize a new optimized RE-MZM. This RE-MZM is fabricated and measured, and predicted results are compared.