As presented in the chapter1, applications of left-handed materials (LHMs) are characterized by simultaneous negative permittivity and permeability in various microwave applications. This concept was extended to the field of transmission lines by UCLA group [CAL 2002]. An equivalent circuit approach was also developed by Eleftheriades and al [ELE 2002]. As a result the concept of Left-Handed Transmission Line (line with a negative phase velocity) was proposed. For practical applications the parasitic Right-Handed (RH) effects naturally occurring in a Left-Handed (LH) structure must be taken into account. Thus, the various proposals have led to the concept of composite right left handed line (CRLH). The CRLH notation is now the usual designation of these artificial lines since the name clearly describes the fundamentally right-handed and left-handed nature of metamaterial lines [CAL 2006].