A Lumped-Element Directional Coupler With High Isolation for Mobile RFID Reader

A lumped-element directional coupler with a high isolation characteristic for mobile RFID reader systems is proposed and experimentally demonstrated. Compared with the conventional lumped-element circuit, the proposed structure utilizes compensation capacitors and achieves a very high isolation despite low quality factor on-chip inductors. It was fabricated on a high-resistivity silicon substrate and showed an isolation of 79 dB, a coupling level of 14.8 dB, and an insertion loss of 1.74 dB at 910 MHz.