Characteristic of impedance

Characteristic impedance refers to the ratio of voltage to current (apparent resistance) when RF signals travel through coaxial cables, and is measured in ohms (Ω). Characteristic impedance is extremely important for efficient signal transmission. When the impedance of the signal source transmitter and receiver matches the characteristic impedance of the coaxial cable, signals are transmitted without loss. If they do not match, part of the signal is reflected, degrading signal quality.
The characteristic impedance (Z0) of a coaxial cable is determined by the cable’s dimensions and the material properties. Specifically, it is calculated using the diameter of the central conductor (D1), the inner diameter of the outer conductor (D2), and the dielectric constant (εr) of the insulator, as shown in the following equation.

Characteristic impedance is an important concept in RF circuit design. Understanding characteristic impedance enables the suppression of signal reflection and the realization of efficient transmission.