Why is 50-ohm characteristic impedance standardized in RF and Microwave systems?

Hardware of most of the RF and Microwave systems is standardized with 50-ohm. Why is this a worldwide standard?

Theory of standardization to 50-ohm came from coaxial cables, which were used in radio transmissions during 1930s. It was a compromise made and a tradeoff between power handling and losses.

A loss vs. characteristic impedance plot of the transmission line provides a better understanding for the standardization of the 50-ohm line. The minimum insertion loss was found at approximately 77-ohms. Another graph was plotted between the power handling vs. characteristic impedance, and it was found that the maximum power was delivered at approximately 30-ohm.

Attenuation (blue curve) is the lowest at 77-ohms, and the  maximum power handling (red curve) is at 30-ohms. There is no mystery with the 50-ohms selection. It is a simple tradeoff calculation. The tradeoff between the loss and power handling for the transmission line was concluded by averaging out the 77-ohm and 30-ohm, which came very close to 50-ohms. Hence, 50-ohms is universally accepted as a standard for all RF and Microwave systems.

Team SimTech

Cadence Design Systems