An Advanced Broadband Absorptive Balun for Modern Communication Systems

This article presents a novel broadband common-mode (CM) absorptive balun developed through an optimization strategy. Different from the conventional Marchand balun that reflects CM waves, the proposed balun excels in mitigating the radio frequency interference issues stemming from the reflected CM noise in high-speed circuits by effectively absorbing these unwanted signals. Meanwhile, by simply adding two slotlines and two resistors on the ground plane of a conventional two-layer Marchand-balun structure, a wide absorbing band is achieved. An equivalent circuit model of the proposed balun is also introduced, and a closed-form CM reflection coefficient is further derived. The equivalent circuit facilitates efficient optimization of key design parameters of the balun structure, negating the need for time-consuming full-wave simulation while ensuring broadband CM-absorptive performance. The proposed balun structure can consistently deliver a wideband CM absorption exceeding 10 dB spanning from 1.3 GHz to 4.2 GHz, which is validated by a full-wave simulation and measurement.