A Dielectric Loss-Based Absorptive Common-Mode Filter Using Transmission Space Separation Structure

Abstract

In this article, a transmission space separation (TSS) structure is proposed to reconcile the contradiction between high loss for common-mode (CM) noise and low loss for differential-mode (DM) signal in the region of resistor-free absorptive CM filter (A-CMF) design. To meet the essential requirement for implementing A-CMF, which should contain nonzero real impedance parts, two matching components based on substrate integrated waveguide (SIW) cavity and defect ground structure (DGS) are employed. For both matching components, their equivalent circuit models (ECMs) are developed, and the impact of key parameters on the resonance points and resistance is discussed in detail. Then, two types of single-band A-CMFs are proposed based on matching components, and the transformation from directional A-CMF to bidirectional A-CMF is also discussed. The proposed A-CMFs can achieve an absorptive band at 5 GHz with absorptions of 97% and 99%, while the DM transmission performances maintain sub-3-dB insertion loss until 8.5 GHz. To meet the requirement of broadband absorption of CM noise, a band-enhanced A-CMF is proposed, fabricated, measured, discussed, and evaluated. The measured and simulated results aligned well with each other. The band-enhanced A-CMF can realize a 0.6-GHz absorption band at 5 GHz and maintains sub-3-dB insertion loss until 8.7 GHz. Furthermore, to examine the portability of TSS structure, the A-CMFs based on substrate integrated suspended line (SISL) and 3-D through-silicon via (TSV) processes are designed. An SISL prototype is fabricated, measured, and evaluated, and good agreement between simulation and measurement results is realized.