A Multiband Directional Coupler Using SOI CMOS for RF Front-End Applications

This letter introduces a novel multiband directional coupler for RF front-end applications. Conventional narrowband directional couplers are widely used for mobile applications because of their compact size. However, excessive power loss due to strong coupling in the higher frequency range severely limits their bandwidth. To resolve this issue, we propose a dual directional coupler employing a coupling switching stage, where the asymmetric coupled lines can be electrically coupled or floated to mitigate severe coupling loss. The proposed coupler has been implemented to an integrated circuit using the silicon-on-insulator process. The measured results showed a considerably enhanced bandwidth from 0.69 to 4 GHz covering the entire frequency band of long-term evolution with a low power loss of less than -0.21 dB in the target frequency range.