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Coaxial cable derives its name from the spatial relationship shared between the center conductor and the outer conductor. Figure 1 shows this "co-axial" positioning of conductors. A British engineer and mathematician by the name of Oliver Heaviside first patented the basic design of coaxial cable in 1880 (Patent Number: 1407). Then in 1929, almost 50 years later, Lloyd Espenshied and Herman Affel of AT&Tís Bell Labs secured a United States patent for the first modern coaxial cable design (US Patent Number: 1,835,031). Soon afterwards, coaxial cable started gaining popularity with radio engineers and became the preferred choice for connecting antennas to transmitters and receivers. As it turns out, coaxial cable is well suited for running up and down metal antenna towers, along gutters, or around any other metal structures since all electrical energy transmits down the interior of the cable and remains isolated from external influences.

In the late 1920s and early 1930s, Bell Labs set out to determine which coaxial impedance value was optimum. Surprisingly, the optimum impedance changes depending on the primary application. By experimentation Bell Labs found 30 ohms is best for high power, 77 ohms is best for low attenuation, and for high voltage 60 ohms turned out to be the best impedance value. Most modern coaxial cables come in 50, 75 or 93 ohm impedances and 50 ohms is by far the most popular impedance choice for high frequency transmission lines.