A coaxial cable is a controlled impedance transmission line used to carry RF, video, and other high frequency electrical signals. It contains a center conductor, a dielectric layer, an outer conductor, and a protective jacket. The dimensions and materials of these layers affect impedance, attenuation, shielding, flexibility, temperature resistance, and connector compatibility. When selecting a coaxial cable, check the system impedance, operating frequency, required length, signal loss, routing space, environment, and connector interface.
What Is a Coaxial Cable
A coaxial cable, often called coax, has an inner conductor and an outer conductor arranged around the same geometric axis. A dielectric material maintains controlled spacing between the two conductors. This structure forms a defined transmission path for high frequency electrical signals.
This configuration forms the basis of the term coaxial, meaning that the inner conductor and the outer conductor share a common axis.
Unlike ordinary hookup wire, coaxial cable is designed around characteristic impedance. The cable geometry and dielectric properties determine how the signal path behaves. The equipment port, cable, connector, and load therefore need compatible impedance throughout the connection.
How Coaxial Cable Construction Controls Performance
Each layer performs a different electrical or mechanical function, and changing one layer can affect several cable specifications at the same time.
| Cable Layer | Main Function | Effect on Cable Selection |
|---|---|---|
| Center conductor | Carries the signal current | Material, diameter, plating, and solid or stranded construction affect resistance, flexibility, power handling, and center contact fit. |
| Dielectric | Maintains spacing between the conductors | Material and dimensions affect impedance, attenuation, velocity factor, phase delay, and temperature capability. |
| Outer conductor and shield | Provides the return path and contains the electromagnetic field | Foil, braid, double braid, solid tube, and corrugated structures affect shielding, flexibility, diameter, and termination. |
| Outer jacket | Protects the internal cable structure | Jacket material affects temperature resistance, moisture resistance, chemical exposure, flame requirements, and routing durability. |
The layers cannot be evaluated independently. Increasing the dielectric diameter may change characteristic impedance. Adding another shield layer may improve shielding but also increase the cable diameter and stiffness. A different jacket may improve environmental resistance while changing the connector rear body or ferrule required for termination.
For a closer look at how these structural choices affect RF performance, review how coaxial cable construction affects impedance, loss, and connector fit.
How Does a Coaxial Cable Carry RF Signals
At high frequencies, signal energy travels through the electromagnetic field formed in the dielectric between the center conductor and the inner surface of the outer conductor. The outer conductor also forms the return current path and limits the amount of energy that can couple into or out of the cable.
The center conductor carries the signal current, while the inner surface of the outer conductor carries the return current.
The conductor dimensions and dielectric properties establish the characteristic impedance of the cable. When the cable, connectors, equipment port, and load follow the same impedance, reflections at each transition can be kept lower.
An impedance change may come from an incompatible connector, mixed 50 ohm and 75 ohm components, damaged dielectric, poor termination, or severe bending near the connector. These changes can increase reflected energy, VSWR, and insertion loss in the finished signal path.
Coaxial Cable vs Coaxial Cable Assembly
A coaxial cable is the unterminated transmission line formed by the center conductor, dielectric, outer conductor, and jacket. A coaxial cable assembly is the finished interconnect after compatible connectors have been terminated at one or both ends of the cable.
The cable datasheet may list impedance, attenuation per unit length, velocity factor, outside diameter, bend radius, and temperature range. Finished assembly performance also depends on total length, connector transitions, strip dimensions, attachment quality, adaptors, and mating interfaces.
Cable attenuation describes loss in the cable body, while finished assembly insertion loss also includes connectors, termination points, adaptors, and mating interfaces. For a more detailed explanation, see our guide to insertion loss in RF cable assemblies.
How to Choose a Coaxial Cable
Start with the requirements of the connected RF system. Confirm the impedance and highest operating frequency first, then check the required cable length and attenuation at that frequency. A cable that works well for a short internal connection may produce too much loss over a longer run.
Mechanical limits matter as well. Check the cable diameter, bend radius, available routing space, connector interface, and whether the cable will remain fixed or move during use. Temperature, moisture, outdoor exposure, and other environmental conditions may also affect the cable and jacket choice.
These checks narrow the available cable options, but the final choice depends on how the electrical and mechanical requirements work together. For a more detailed selection process, see how to choose a coaxial cable for RF systems.
Where Is Coaxial Cable Used
Coaxial cable carries RF, video, and measurement signals where impedance control and shielding are required. However, the application name alone cannot determine the correct cable. The actual cable depends on the electrical path and the installation conditions.
Antenna and Wireless Equipment
Coaxial cable connects antennas to wireless modules, radio equipment, routers, gateways, base stations, and other communication devices. Short internal antenna links usually require a small cable diameter and flexible routing, while longer outdoor feeds place more weight on attenuation and weather resistance.
Test and Measurement Equipment
Test systems use coaxial cables to connect signal generators, spectrum analyzers, network analyzers, oscilloscopes, fixtures, and devices under test. Depending on the measurement, the cable may need controlled insertion loss, low VSWR, stable phase, repeated mating capability, or resistance to frequent movement.
A general RF cable may carry the signal successfully but still be unsuitable for repeatable measurement work. The complete assembly, including the cable, connectors, adaptors, and strain relief, needs to match the test method.
Communication and RF Distribution Systems
Coaxial cable is used to distribute signals between antennas, radios, amplifiers, splitters, filters, cabinets, and communication equipment. Longer routes increase total cable loss, while additional connectors and adaptors introduce more transitions into the signal path.
The cable needs to support the required frequency, power, shielding, environmental conditions, and installation method without exceeding the available loss budget.
Video and Broadcast Systems
Video and broadcast systems commonly use 75 ohm coaxial cable. In these systems, the cable, connectors, equipment ports, splitters, and other signal path components need to maintain the specified impedance.
The correct cable also depends on video bandwidth, transmission length, installation environment, shielding requirements, and the connector interface used by the equipment.
FAQ
Conclusion
A coaxial cable uses a center conductor, dielectric, outer conductor, and jacket to create a controlled signal path for high frequency transmission. Its construction affects impedance, shielding, attenuation, flexibility, and connector compatibility, while the performance of a finished RF cable assembly also depends on the connectors and termination at each end. If you are reviewing a coaxial cable for an antenna, instrument, communication device, or other RF connection, you can share the operating frequency, impedance, required length, connector interfaces, and routing limits with the Bafitop team for cable and termination review.