Cut-Off Frequency

The cut-off frequency of a coaxial cable is that frequency at which modes of energy transmission other than TEM (Transverse Electro-Magnetic) mode can be generated. It does not mean that the TEM mode becomes highly attenuated. This frequency is a function of the mean diameter of the conductors and the velocity of propagation of the cable. The higher modes are only generated at impedance discontinuities and in many situations the cable can be operated above the cut-off frequency without substantial VSWR or insertion loss increase.