In microwave theory, TEM mode stands for Transverse Electromagnetic Mode. It is one of the fundamental electromagnetic modes that can exist in a transmission line or waveguide.
In a TEM mode, the electric field (E) and magnetic field (H) vectors are both transverse to the direction of propagation. This means that the electric and magnetic fields are perpendicular to each other and perpendicular to the direction the wave is traveling. There is no component of the fields parallel to the direction of propagation.
In a transmission line or waveguide supporting a TEM mode, the electric and magnetic fields oscillate in a coordinated manner, propagating energy along the transmission line without any attenuation. This mode is often used in many practical microwave and radio frequency applications, such as coaxial cables, microstrip lines, and certain types of waveguides, as it ensures efficient energy transmission with minimal losses.
For a waveguide or transmission line to support a TEM mode, it must have a minimum of two conductors separated by a dielectric medium, ensuring that the electric and magnetic fields can propagate without coupling to the environment outside the guide.