This paper proposes a novel approach to designing materials with negative refractive indices using periodically loaded transmission lines. The authors exploit the well-known L-C distributed network representation of homogeneous dielectrics, where the conventional low-pass topology has positive equivalent permeability and permittivity. By interchanging the positions of L and C, the dual configuration results in simultaneously negative material parameters. Two-dimensional periodic versions of these dual networks are used to demonstrate negative refraction and focusing, which are manifestations of the backward harmonic propagation in such media. The characteristics of these artificial transmission-line media are presented, along with a method for implementing them in planar form. Circuit and full-wave field simulations illustrate negative refraction and focusing, and the first experimental verification of focusing using a planar implementation is provided. The proposed media support two-dimensional wave propagation and are well-suited for RF/microwave device and circuit applications. The design process involves modifying the discrete loading elements to account for the effects of finite-length transmission lines, ensuring accurate propagation constant and refractive index values. The experimental results confirm the effectiveness of the proposed design, demonstrating near-field focusing over an octave bandwidth and an electrically short area.This paper proposes a novel approach to designing materials with negative refractive indices using periodically loaded transmission lines. The authors exploit the well-known L-C distributed network representation of homogeneous dielectrics, where the conventional low-pass topology has positive equivalent permeability and permittivity. By interchanging the positions of L and C, the dual configuration results in simultaneously negative material parameters. Two-dimensional periodic versions of these dual networks are used to demonstrate negative refraction and focusing, which are manifestations of the backward harmonic propagation in such media. The characteristics of these artificial transmission-line media are presented, along with a method for implementing them in planar form. Circuit and full-wave field simulations illustrate negative refraction and focusing, and the first experimental verification of focusing using a planar implementation is provided. The proposed media support two-dimensional wave propagation and are well-suited for RF/microwave device and circuit applications. The design process involves modifying the discrete loading elements to account for the effects of finite-length transmission lines, ensuring accurate propagation constant and refractive index values. The experimental results confirm the effectiveness of the proposed design, demonstrating near-field focusing over an octave bandwidth and an electrically short area.