Effective electromagnetic parameters of novel distributed left-handed microstrip lines

The novel one-dimensional left-handed microstrip lines (LHMLs) consisting of the arrays of thin wires and two-layer split-ring resonators are investigated theoretically and experimentally in this paper. Unlike the conventional left-handed metamaterials for waveguides or microstrip lines, which are bulky three-dimensional constructions or require the lumped elements for high-pass configuration, this distributed structure can be directly implemented on a substrate by photolithographic techniques without soldering any chip inductors or capacitors. Moreover, it can also be easily realized at a higher frequency region by scaling the dimensions of the structure, making it highly efficient and flexible in millimeter-wave applications. To characterize the inhomogeneous LHML, the effective medium description is developed for extracting the effective electromagnetic parameters, i.e., the complex effective permittivity and permeability, as well as the refractive index. Results show that not only the simultaneously negative real permittivity and permeability, but also the antiparallel phase and group velocities may be achieved in the design passband region. In contrast to the antenna array using the conventional microstrip delay line, the LHML is incorporated in the series-fed microstrip combline array to exhibit the leading phase between the successive elements.