Similarly, at operation 34, determining the value for the second set of feature sizes D1, D2, W and S for a second one of the pair of small loop transmission coils 22 according to the first loop's size is performed. Supplying the second set D1, N, W and S values to the formula (2) in FIG. 3B, a value of inductance L2 can be obtained. Further, supplying the Lloop2 value to the formula (1) in FIG. 3A at operation 35, given that the resonant frequency f of the small loop is 6.78 MHz, a value of series capacitance C2 for the second small loop transmission coil 22 can be obtained. At operation 36, a simulation model in the HFSS is utilized to fine tune the second capacitance C2 based on a working distance between the primary coil antenna 21 and the phone with the metallic cover and/or case (the target device, particularly the secondary antenna coil of the target device, the PRU antenna 25 shown in FIG. 5B). The working distance is set according to a customer's/user's requirements. The simulation model in the HFSS can determine the optimal gap size between the first and second ones of the pair of small loop transmission coils 22.
