A Metamaterial-Typed Differential Transmission Line with Broadband Common-Mode Suppresssion

A differential transmission line using a negative permittivity metamaterial is proposed with the intrinsic characteristic of wideband common-mode suppression. Based on the transmission line theory, a dispersion diagram is derived from the corresponding equivalent circuit model. It manifests that in the structure, the differential mode can propagate at all frequencies, while the common mode can only evanesce at some frequency ranges. A practical structure is implemented in a low temperature co-fire ceramic (LTCC) fabrication technology. The common-mode insertion loss of the structure can attain over 20 dB from 5.2 GHz to 10 GHz with fractional bandwidth of 63 % and the good differential signal quality is kept. A novel differential transmission line is proposed with the unique performance of broadband common-mode suppression. It is very useful in the application of GHz differential circuits.