A Bidirectional Absorptive Common-Mode Filter Based on Interdigitated Microstrip Coupled Lines for 5G “Green” Communications

This paper proposes a bidirectional absorptive common-mode filter (A-CMF) for 5G “green” communication systems. The A-CMF is a balanced-to-balanced structure using interdigitated coupled lines to replace normal double parallel-coupled lines for enhanced coupling and easy manufacturing. The resistors are introduced to dissipate the common-mode (CM) noises into heat and thus to avoid the noises being reflected and still existing in the communication system. This novel A-CMF features an intrinsic CM noises absorption while maintaining its differential-mode (DM) filtering characteristics. As a proof-of-concept demonstration, one microstrip prototype is fabricated in a two-layer printed circuit board (PCB) and the measurements are consistent with the simulations. The DM signals can pass through this A-CMF without being attenuated from 1.38 GHz to 5.19 GHz but the CM noises are suppressed throughout the broad frequency range between 0.72 GHz and 8 GHz. It is worth noting that this A-CMF realizes a wide band with 90% absorption efficiency of CM noises from 2.18 GHz to 4.97 GHz.