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.
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(9.216) |
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(9.217) |
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(9.218) |
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(9.219) |
The S-parameters (according to the port numbering in fig. 9.12) are as followed [11].
reflection coefficients
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(9.220) |
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(9.221) |
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(9.222) |
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(9.223) |
with the denominator
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(9.224) |
and
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(9.225) |
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(9.226) |