The figure on the right presents a structure referred to as a series node. It describes a block of space dimensions Δ Δ x , Δ Δ y and Δ Δ z that consists of four ports. L ′ and C ′ are the distributed inductance and capacitance of the transmission lines. It is possible to show that a series node is equivalent to a TE-wave, more precisely the mesh current I, the x -direction voltages (ports 1 and 3) and the y -direction voltages (ports 2 and 4) may be related to the field components H z , E x and E y . If the voltages on the ports are considered, L x = L y , and the polarity from the above figure holds, then the following is valid