An RF cable carries radio frequency signals between parts of an RF system, such as antennas, wireless modules, radios, test equipment, and other signal interfaces. In most cable-based RF interconnections, the signal path uses coaxial construction to maintain controlled impedance, limit unwanted radiation, and protect the signal from external interference. Understanding the cable structure and its main specifications makes it easier to distinguish the cable itself from a finished RF cable assembly.
What Is an RF Cable
RF stands for radio frequency. An RF cable is an electrical transmission cable intended to carry signals within a radio frequency range between two points in a system. The term describes what the cable is used for, while the cable construction describes how the signal path is physically formed.
For many RF connections, the cable is coaxial. A coaxial RF cable places a center conductor and an outer conductor around the same axis, with a dielectric material separating them. This controlled geometry allows the cable to maintain a defined characteristic impedance and provides a shielded transmission path for RF energy.
RF Cable vs Coaxial Cable
RF cable and coaxial cable describe two different aspects of a cable. RF refers to the signal application, while coaxial refers to the physical arrangement of the conductors. Because coaxial cable is a common transmission structure for RF signals, the terms are often used together as RF coaxial cable.
They are closely related, but they are not strict synonyms. A coaxial cable describes a physical transmission line structure, while RF describes the signal application. On this page, RF cable refers mainly to coaxial cable used for RF interconnection.
RF Cable vs RF Cable Assembly
An RF cable is the cable itself. An RF cable assembly is a finished interconnection that combines a defined cable length with compatible RF connectors or adaptors at one or both ends. The assembly may also include heat shrink, boots, labels, strain relief, sealing parts, or other mechanical features according to the required construction.
This distinction matters when reading specifications. A bulk cable datasheet describes properties such as characteristic impedance, attenuation, diameter, dielectric material, shielding construction, and bend radius. Finished assembly performance can also depend on connector interfaces, termination quality, total length, adaptors, and the way the complete path is tested.
How an RF Coaxial Cable Is Built
A typical RF coaxial cable contains four main structural elements: the center conductor, dielectric, outer conductor, and outer jacket. Each layer has a different electrical or mechanical function, and their dimensions and materials work together to define the behavior of the cable.
| Cable Part | Main Function | What It Can Affect |
|---|---|---|
| Center conductor | Carries RF signal current | Conductor loss, flexibility, power handling |
| Dielectric | Maintains controlled spacing between conductors | Impedance, velocity of propagation, dielectric loss |
| Outer conductor or shield | Provides the RF return current path and shielding boundary | Shielding, return path, impedance consistency |
| Outer jacket | Protects the cable mechanically and environmentally | Abrasion resistance, temperature range, UV and moisture exposure |
Center Conductor
The center conductor carries the RF signal current. Depending on the cable design, it may be solid or stranded and may use copper or another conductive material selected for the required electrical and mechanical properties. Conductor material, diameter, and operating frequency all affect conductor loss.
Dielectric
The dielectric electrically separates the center conductor from the outer conductor and keeps their spacing controlled along the cable. Characteristic impedance is established by the conductor geometry together with the electrical properties of the dielectric, so the dielectric material alone does not determine impedance.
The dielectric also affects propagation velocity and dielectric loss. Materials and construction methods vary between cable families, so two cables with the same nominal impedance can still have different attenuation, dimensions, temperature limits, and mechanical behavior.
Outer Conductor and Shield
The outer conductor forms the RF return current path and surrounds the dielectric to create the coaxial transmission structure. It also limits electromagnetic energy from entering or leaving the cable. Depending on the design, the outer conductor may use braid, foil, multiple shield layers, a solid metal tube, or a corrugated metallic structure.
Outer Jacket
The outer jacket protects the internal cable structure from abrasion, handling, chemicals, temperature, sunlight, and moisture exposure according to the selected material. Jacket material does not define RF performance by itself, but it affects whether a cable can be installed and maintained in the intended environment.
Common RF Cable Construction Types
RF coaxial cables are available in several construction families. RF coaxial cables can be grouped by physical construction and routing behavior. Common families include flexible, semi-rigid, conformable, micro-coaxial, and corrugated designs.
Flexible Coaxial Cable
Flexible coaxial cable commonly uses a braided or combined foil and braid outer conductor. It can be routed through equipment, enclosures, antenna connections, and other paths that require the cable to bend during installation. Cable diameter, conductor construction, braid structure, dielectric, and jacket vary considerably between flexible cable families.
Semi-Rigid Coaxial Cable
Semi-rigid coaxial cable uses a solid metallic outer conductor that holds its shape after forming. The stable geometry can provide consistent shielding and electrical behavior in fixed RF and microwave paths. It is normally formed to the required route and is not intended for repeated flexing after installation.
Conformable Coaxial Cable
Conformable coaxial cable provides a middle ground between standard flexible cable and semi-rigid construction. It can be shaped more easily during installation while retaining a more controlled route than a highly flexible cable. The permitted bend and forming limits still depend on the selected cable specification.
Micro-Coaxial Cable
Micro-coaxial cable uses a very small outside diameter where routing space is limited. The reduced size can make internal routing easier, but attenuation, shielding, connector compatibility, mechanical strength, and permitted bend radius need to be checked for the selected construction.
Corrugated Coaxial Cable
Corrugated coaxial cable uses a corrugated metallic outer conductor that combines a relatively large cable structure with controlled flexibility. It is commonly considered for longer RF feeder paths and installations where attenuation, shielding, mechanical strength, and power handling need to be evaluated together.
Key Specifications That Define RF Cable Performance
Characteristic Impedance
Characteristic impedance is the ratio of voltage to current for a travelling wave in a transmission line. RF coaxial cables commonly include 50 ohm and 75 ohm designs, although other impedance values also exist. The cable, connectors, and connected interfaces need compatible impedance when they form a complete RF path.
Frequency Range
Frequency capability depends on the complete cable construction and, for a finished assembly, the connector interfaces and termination. A cable name by itself does not provide a universal frequency limit for every finished RF cable assembly.
Attenuation
Attenuation shows how much signal is lost as it travels through the cable and is normally specified in decibels over a defined length at a defined frequency. Attenuation generally increases as frequency or cable length increases, so a meaningful loss value needs both frequency and length conditions.
Shielding
Shielding construction affects how well the cable contains its RF energy and resists external electromagnetic interference. Flexible cables may use braid, foil, or multiple shield layers, while semi rigid and corrugated cables use metallic outer conductor structures. Shield type and coverage need to be read from the specification of the exact cable.
Cable Diameter and Bend Radius
Cable outside diameter affects routing space, connector termination dimensions, and mechanical handling. Minimum bend radius describes how tightly a particular cable may be routed without exceeding its specified mechanical limit. It does not describe repeated flex life, and the exact value depends on the selected cable construction.
Temperature and Environmental Rating
Temperature range, jacket material, moisture protection, UV resistance, chemical exposure, and mechanical protection describe whether a cable can tolerate a particular environment. These values belong to the exact cable specification and cannot be inferred reliably from a general RF cable category.
FAQ
Conclusion
An RF cable is defined by its role in carrying radio frequency signals, while its coaxial construction determines how the transmission path is physically formed. Center conductor geometry, dielectric properties, outer conductor structure, impedance, attenuation, shielding, cable size, bend radius, and environmental limits all help describe how a specific cable will behave. The cable itself also needs to be distinguished from a finished RF cable assembly with connectors and a defined length. If you are checking an RF cable type, cable construction, connector interface, or assembly specification and need help confirming the details, you are welcome to contact Bafitop anytime.