Editing Transverse mode (section)

====Conductor-based transmission lines====
In [[coaxial cable]] energy is normally transported in the fundamental TEM mode. The TEM mode is also usually assumed for most other electrical conductor line formats as well.  This is mostly an accurate assumption, but a major exception is [[microstrip]] which has a significant longitudinal component to the propagated wave due to the inhomogeneity at the boundary of the dielectric substrate below the conductor and the air above it.
Inhomogeneity also occurs at connectors or bends in a coaxial cable. Non-TEM modes created by connectors are usually negligible unless the signal has a high enough frequency. This is referred to as maximum '''extraneous-mode-free operation'''<ref>{{cite journal |last1=Eisenhart |first1=R. L. |title=A novel wideband TM01-to-TE11 mode converter |journal=998 IEEE MTT-S International Microwave Symposium Digest (Cat. No.98CH36192) |date=1998 |volume=q |pages=249–252}}</ref> or simply '''mode-free operation'''<ref>{{cite web |last1=Hannon |first1=Michael J. |last2=Malloy |first2=Pat |title=Application Guide to RF Coaxial Connectors and Cables |url=https://www.globalspec.com/ARRFMicrowaveInstrumentation/ref/appnote51B.pdf |access-date=26 February 2025}}</ref><ref>{{cite web |last1=hobbs |title=What does "mode-free" mean, in the context of coaxial connectors? |url=https://electronics.stackexchange.com/q/575353 |website=Electrical Engineering Stack Exchange |access-date=26 February 2025 |date=14 July 2021}}</ref> frequency of the connector.

In an optical fiber or other dielectric waveguide, modes are generally of the hybrid type.