Differential and singleended impedances
Assuming that the propagation speed of TEM wave is constant:
the even and odd mode impedances are:
where Z_{0} is the characteristic impedance of each line:
and ξ is a parameter that indicates the strength of coupling:
Conversely,

We will derive the relation between differential and singleended impedances.
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First, we will derive the relation among capacitances C_{s}, C_{m} and C.
Assuming the line1 exists alone with linecharge q_{1}, its voltage is:
Superposing the electric field of the line2 charged with q_{2}, the line1 voltage can be expressed with a parameter ξ:
Because the line1 and line2 are identical, the line2 voltage is similarly expressed:
If the line1 and line2 voltages are held at v_{1} and v_{2}, the linecharges are:
Comparing the coefficients of two equations, we obtain the relation among C_{s}, C_{m} and C:
Noting that C_{s}≦C and 0<C_{m},C because of physical implications, then
Solving eq. (2) for the positive ξ:
This parameter ξ increases according to C_{m}/C, so it indicates the strength of coupling.
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In the previous section, we have expressed Z_{±} and u_{±} in terms of L,L_{m},C_{s},C_{m}:
Inserting (1) and (2), we obtain the expression of Z_{±} and u_{±} in terms of L,L_{m},ξ:
where Z_{0} and u is the characteristic impedance and propagation speed of each line:
Although u_{+ }and u_{−} look different from each other, the propagation speed of TEM wave must be a constant, that is the light speed. So assuming
, the inductances are also expressed by the parameter ξ:
Then we can simply express the even and odd mode impedances in terms of Z_{0} and ξ :
Noting 0≦ξ<1 because of physical implications, then
Conversely, Z_{0} is the arithmetic average of Z_{+} and Z_{−}, and ξ is the relative difference between Z_{+} and Z_{−}：