The characteristic impedance of a coaxial cable is a key parameter for ensuring proper signal transmission in applications like telecommunications and RF (radio frequency) systems. The characteristic impedance is typically specified by the cable manufacturer and is an essential consideration for matching impedances in signal transmission systems to prevent signal reflections and loss.

The characteristic impedance, denoted by z0 is a measure of how much opposition the cable presents to the flow of electrical signals and is crucial for ensuring proper signal transmission in various applications.

The characteristic impedance of a coaxial cable is determined by the physical dimensions and properties of the cable's construction, specifically the relationship between the inner and outer conductors, as well as the dielectric material between them. The formula for the characteristic impedance of a coaxial cable is given by:

Where,

d = The outside diameter of the inner or center conductor.

D = Inside diameter of the shield.

εr = Dielectric constant of the insulator.

Z0 = Characteristic impedance.

Apart from the characteristic impedance, other important parameters of a coax cable is cut-off frequency, denoted by fc.

In the area of microwave and milli-wave communications, the cut-off frequencies play an important role. Further, the capacitance C value is a function of εr and is given by the following formula:

Similarly, the Inductance L of the coax cable per unit length is given by the following formula:

A calculator is available at rfcables.org, a website specializing in rf and microwave aggregator services. Checkout the Co-ax Impedance Measurement Tool.