Conceptually you can import a circuit model for your device to an other circuit analysis tool. Concerning the equivalent circuit of an antenna, there is a physical model of such dipole antennas. If they are resonant, then their input impedance is equivalent to a parallel LC resonance circuit in addition to the losses represented as a resistance shunting the parallel LC circuit. This resistance is the radiation resistance. In case of matching the source resistance feeding the antenna must be equal to the radiation resistance for maximum power transfer condition from source to antenna.