Analysis of a directional coupler using magnetic/dielectric hybrid transmission-line for cellular phone

Transmission characteristics of a directional coupler with a magnetic/dielectric thin film hybrid structure was analyzed on the basis of 3D electromagnetic field analysis. The device consisted of an inner dielectric/magnetic/dielectric sandwich structure, the top coupled signal lines, coupling capacitance composed of top rectangular electrode, and bottom ground plane. Both electric field coupling and magnetic field coupling between top signal lines were controllable by changing electrode size of coupling capacitance and spacing between top signal lines, respectively. From the numerical calculation of the signal transmission characteristics, an insertion loss was less than 0.6 dB, and signal directivity was more than 15 dB in the frequency range of 0.8-2 GHz used in the cellular phones.