In figure 11 Rac1 and Rac2 represent coil losses and M stands for the mutual inductance between the coils. In addition, Rs is an internal source impedance and RL , the load impedance. Cext1 and Cext2 represent the external capacitors connected to the antennas (internal capacitance of the coil is neglected). Supposing that Rs=RL and the coils are the same (due to the equivalence of coils, subscripts 1,2 are omitted in following discussion).