The attenuation is described in the 2D Extractor help:
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/Electronics/v232/en/home.htm%23../Subsystems/Q3DExtractor/Content/Q3D/ModalAnalysisofLossyTransmissionLines.htm?TocPath=Q3D%2520Extractor%257CQ3D%2520Extractor%2520Help%257C2D%2520Extractor%2520Technical%2520Notes%257CTransmission%2520Line%2520Circuit%2520Models%257CDistributed%2520Models%2520for%2520Transmission%2520Lines%257CLossy%2520Transmission%2520Lines%257C_____1
The propagation constants γn are complex numbers with real part αn and imaginary part βn.
It can be seen that αn represents the attenuation per unit length that the mode experiences as it moves down the transmission line. The imaginary part βn represents the change in phase per unit length.
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