TEMmodi

TEMmodi is a term used in electrical engineering to denote the family of transverse electromagnetic propagation modes in multi-conductor transmission lines and related planar structures. The phrase is commonly encountered in technical literature that discusses how signals propagate along coaxial cables, shielded pairs, microstrip, and other two- or multi-conductor geometries. In an ideal lossless dielectric with perfect conductors, a TEM mode has electric and magnetic fields entirely transverse to the direction of propagation, so there is no cutoff frequency and the wave impedance is Z0 = sqrt(μ/ε).

In multi-conductor systems, TEMmodi encompasses the various field distributions that are approximately TEM in the sense of having predominant transverse fields, with different relative phasing among conductors. In planar structures such as microstrip, true TEM cannot always exist over all frequencies, but quasi-TEM or near-TEM modes behave similarly at lower frequencies and are often grouped under TEMmodi in design contexts.

Applications include high-frequency interconnects, broadband RF links, and impedance-controlled network design. Key examples are coaxial cables, shielded twisted pairs, and differential microstrip lines.

Limitations include conductor and dielectric losses, finite conductor thickness, and dielectric inhomogeneity, which introduce longitudinal field components and dispersion, causing deviations from the ideal TEM description.

See also: Transmission line, TEM mode, quasi-TEM, TE/TM modes, coaxial cable, microstrip.