FIG. 1B illustrates a wireless charging device having a coil antenna with a small loop transmission coil design according to the prior art;

FIGS. 2A-2C illustrate a structure of a wireless charging device including a coil antenna with pairs of small loop transmission coils, and FIG. 2D illustrates a blown up view of one of the pairs of small loop transmission coils, according to an embodiment of the invention;

FIGS. 3A-3C illustrate a cross sectional diagram of the wireless charging device and formulae for obtaining resonant frequency and inductance for the coil antenna with small loop transmission coils shown in FIGS. 2A-2D;

FIG. 3D is a flowchart for obtaining parameters of the charging system shown in FIGS. 2A-2C;

FIGS. 4A-4D illustrate an observation line of the coil antenna and the strength of an H (magnetic) field which is enhanced by using the charging system shown in FIGS. 2A-2C when a phone with a metallic cover and/or case is placed at different heights above the charging system;

FIGS. 5A and 5B illustrate a comparison between two different design structures, one where the coil antenna has and one without small loop transmission coils placed under the primary coil antenna;

FIG. 5C shows the coupling efficiency for the primary coil antenna with and without the small loop transmission coils;