Microstrip coupled line filter elements as CRLH transmission line unit cells

Left handed transmission lines have anti-parallel phase and group velocities, unlike right handed transmission lines with positive phase and group velocities. The propagation characteristics show that backward wave propagation occurs in a Left handed transmission line. A composite Right Left Handed (CRLH) transmission line can be constructed using lumped elements or split rings. Using microstrip coupled lines also the CRLH transmission lines can be designed. This paper discusses the backward propagation characteristics of CRLH lines using two different unit cells. One unit cell comprises of lumped elements loading a pure right handed transmission line. The second unit cell comprises of coupled line all stop microstrip filter element. In both the cases the backward propagation is verified using ?? - ?? diagrams and S-parameters.