Negative-Refractive-Index Transmission Lines With Expanded Unit Cells

A new "expanded" negative-refractive-index transmission line (NRI-TL) metamaterial unit cell is introduced. This expanded unit cell minimizes the number and reduces the size of the shunt inductors needed to achieve a certain phase-shift per unit length. As in standard NRI transmission lines, both backward and forward bands are supported, with the possibility of closing the stopband between these two bands. The reduction of the shunt inductors is especially advantageous for microstrip realizations. However, this advantage comes at a tradeoff with bandwidth. An example structure is designed and fabricated in microstrip and the measured results show good agreement with simulations.