 Alternating-impedance transmission line

A periodic lossless line can consist of equal-length sections with impedances $Z_1,Z_2$. Its semi-infinite input is a fixed point of the two-section impedance transformation. The physical solution selects a forward-energy or decaying Bloch wave. At special frequencies where the cell matrix is the identity, the fixed-point equation alone loses uniqueness; limiting absorption or a termination specifies the response.