### Reflectance of an Impedance

Let denote the driving-point impedance of an arbitrary
continuous-time LTI system. Then, by definition,
where and denote the Laplace transforms
of the applied force and resulting velocity, respectively.
The wave variable decomposition in Eq.(C.74) gives

We may call the

*reflectance*of impedance relative to . For example, if a transmission line with characteristic impedance were terminated in a lumped impedance , the reflection transfer function at the termination, as seen from the end of the transmission line, would be .

We are working with reflectance for *force waves.*
Using the elementary relations Eq.(C.73), *i.e.*,
and
, we immediately obtain the corresponding
*velocity-wave reflectance:*

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Passive Reflectances

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Power-Normalized Waveguide Filters