A wide differential passband filter with common-mode suppression property based on left handed metamaterial transmission line

In this paper a wide passband filter with common-mode suppression based on left handed metamaterial transmission line at GHz frequencies is proposed. The concept presented in this work is validated by 3D full-wave electromagnetic simulations. The proposed filter includes a periodic structure which is loaded by series and shunt resonators. The overall structure causes negative magnetic permeability for even mode excitation, yielding an ultra-wide stopband for common-mode signals. Additionally, the structure makes simultaneously negative electrical permeability and magnetic permeability for odd mode excitation that introduce a wide passband filter with bandwidth of 5 to 7 GHz. The analysis is based on transmission line theory and Bloch-Floquet theorem, consequently dispersion relations and wave propagation properties have been derived. The periodic structure consists of 5 unit cells and the overall device size is 0.283 λg ×0.377 Ig with a real size of 7.5 mm ×10 mm. Rogers 4003 with dielectric constant of 3.55 is chosen as substrate of the device. By using the proposed filter, common-mode suppression level of over 30dB is obtained from DC to 16GHz. While suppressing common-mode noise, the filter can also be used as a high selective and low insertion loss passband filter for differential-mode signals. Insertion loss of the desired differential signals is less than 2dB. Comparing with previous works the physical realization of the structure can be simpler and cheaper. It is a 3-layers PCB with straightforward geometry without via utilization.