Generalized Lattice Network-Based Balanced Composite Right-/Left-Handed Transmission Lines

Artificial transmission lines based on lattice network unit cells can mimic the behavior of actual metamaterial transmission lines without introducing any stopband, as opposite to their conventional counterparts based on T- or II-network unit cells, which can be balanced to suppress the stopbands in the transitions from left- to right-handed bands, but will always present stopbands in the right-handed-to left-handed-band transitions. The aim of this paper is twofold. First, the general properties of lattice network unit cells are discussed using simple circuit theory concepts. As a result, a systematic classification of all possible balanced lattice network-based artificial transmission line unit cells is described. Second, a novel multiband lattice network-based unit cell is presented. The proposed unit cell is made up of a coupled-microstrip section in a host microstrip and requires neither air bridges nor via-holes. Coupled lines have already been used to obtain composite right-/left-handed transmission lines, but a solution, based on wiggly lines, is given in this paper to the problem caused by the different even- and odd-mode phase velocities. As a result, the wideband capabilities of the artificial transmission line are fully exploited, as the theoretical and experimental results corroborate.