- 2068 Baisakh · 3 marks
Short note: TEM
Short answer
TEM waves have E_z = H_z = 0 with E, H, and propagation mutually perpendicular. They have no cutoff, propagate from DC with phase velocity v = 1/√(με) (non-dispersive), and require at least two conductors; a hollow waveguide cannot support them.
Write a short note on TEM.
A TEM (transverse electromagnetic) wave is a wave in which both the electric and the magnetic field lie entirely in the plane transverse to the direction of propagation: E_z = 0 and H_z = 0. E, H and the direction of travel are mutually perpendicular.
Properties:
- No cut-off frequency: it can propagate from DC upward.
- Phase velocity v = 1/√(με), independent of frequency, so it is non-dispersive.
- Intrinsic (wave) impedance η = √(μ/ε) = E/H (377 Ω in free space); on a line, the wave appears as voltage and current waves with Z₀ = √(L/C).
- The transverse field distribution is the same as a static field with the same boundary conditions.
Occurrence:
- Uniform plane waves in free space or a lossless dielectric.
- Waves on two-conductor transmission lines such as coaxial cable, parallel-wire lines and stripline (microstrip, with its mixed air-dielectric cross-section, supports only a quasi-TEM wave).
A TEM mode needs at least two conductors, so a hollow single-conductor waveguide cannot support it and carries TE or TM modes instead.
✓ Answer checked by Claude Opus 5.5 (high effort)