This paper investigates the feasibility of using a commercial numerical electromagnetic solver to completely model a MEMS reconfigurable patch antenna taking into account not only the switch RF characteristic but also the influence of the MEMS encapsulation and DC actuation circuit on antenna performance in terms of impedance and radiation pattern. The antenna test configuration is based on a square patch with a single slot, the MEMS being used to either short or leave the slot open, enabling to switch between two operating frequencies while maintaining good input impedance match and stable radiation characteristics. An antenna prototype was fabricated and measured. The obtained good agreement between measurements and simulation confirms the proposed procedure.