A coupled transmission line is described by two identical transmission line ABCD-matrices, one for the even mode (or common mode) and one for the odd mode (or differential mode). Because the coupled lines are a symmetrical 3-line system, the matrices are completely independent of each other. Therefore, its Y-parameters write as follows.
(9.216) | ||
(9.217) | ||
(9.218) | ||
(9.219) |
The S-parameters (according to the port numbering in fig. 9.12) are as followed [11].
reflection coefficients
(9.220) |
(9.221) |
(9.222) |
(9.223) |
with the denominator
(9.224) |
and
(9.225) | ||
(9.226) |