Radio Frequency cables are significant components of every RF system ranging from RF transceiver systems to the aviation industry. What are the major specifications of RF test cables and applications?
RF test cables are used to make efficient signal (power) transfer between two equipment, or devices or to a transmitting antenna. Choosing a proper cable is an important step to make sure the system works efficiently. There are many types of RF cables for specific uses; they mainly vary in their specifications.
Specification of RF Cables
1. Impedance Specification
Characteristic impedance is one of the most important specifications of RF cables. The impedance of a line is determined by the ratio of voltages and the current of a wave transmitting (propagating) along that line. The factors affecting characteristic impedance are the conducting material, dielectric, and geometry of the material.
SI unit of characteristic impedance is Ohm. There are mainly two categories of cables in terms of the characteristic impedance.
50 Ohm cables: used in high-precision RF test equipment and high-frequency applications.
75 Ohm cables: used in domestic video applications, digital audio, and TV distribution networks.
The impedance of a standard RF cable is independent of its physical length. However, cable losses are higher with an increase in length.
2. Frequency Specification
Frequency range is another important specification of RF cables. RF cables are often designed to operate at a specific frequency range due to the limitation of material used for construction. It doesn’t offer required performance outside the specified frequency range (impedance, loss, phase stability, etc…).
Most of the RF cable performance is frequency dependent. Professional RF test applications require higher accuracy for measurement results. High-end cables are usually preferred in RF test and measurement applications.
Find more about Radio Frequency Bands and their applications
3. Phase Stability
In RF testing, phase stability is also a significant parameter that determines the accuracy of the test system. Standard RF cable should have good phase stability; the position of the cable after calibration should not affect phase difference.
In transmission systems, phase differences cause the efficiency of the overall system.
4. Attenuation Specification
Attenuation of the cable is the amount of signal loss due to cable losses/attenuation which is also a qualifying factor of a standard RF cable. Cables with higher losses always affect the entire system’s efficiency.
RF test labs will use low-loss standard RF cables for device measurements.
5. Power Specification
Standard RF cable is developed to operate within a specific power range to ensure safety and efficiency. Wide ranges of RF cables are available to fit applications ranging from low-power transmission, medium-power RF test applications, and high-power cables for transmission and testing purposes.
High-power broadcasting stations and mobile transmitters use high-end cables that can handle power up to a few kilowatts.
In low power applications maximum power rating is also specified as maximum voltage rating.
6. Temperature Stability
Temperature stability becomes an important parameter for high-temperature applications. Engineers have to ensure the accuracy of the measurement setup and make sure cable characteristic has no contributions to the test results.
Most of the co-axial cable has different characteristics under high temperatures and low temperatures. The unusual behavior of the cable might be interpreted wrongly as the performance of the device under test (DUT).
Cables designed for high-temperature applications use materials (dielectric, inner conductor, outer layer, and connector assembly) that handle higher temperatures. Deformation of cables is a common issue during high-temperature tests.
7. Physical dimensions
Dimension of RF cable is yet another specification that determines the connector type, size, shape, physical diameter, and length.
Connector type: many types of RF connectors used in industries depend on frequency range and type of applications.
BNC: used in low-frequency low power applications
SMB: used in mid frequency low power applications
SMA: used in high-frequency high-power applications
N-type: used in high-frequency high-power applications
Flexibility: cable flexibility requirements vary according to applications. Some application requires rigid cables which are permanently fixed after implementation. RF test equipment requires a cable with flexibility and stable performance for many cycles.
Application of RF cables
- Radio communication systems
- Mobile communication networks
- Domestic applications, digital audio, and TV channel distribution network
- Professional RF test and measurement systems, labs, and development units
- Aerospace industry for accurate communication equipment
- Wired telephone and communication networks
- Military and space application
- Ships and navy communication systems
- Satellite communications
- RF equipment in medicine and healthcare
How to choose a proper RF cable
RF cables are designed to perform application specific. Some applications require higher accuracy and other requires higher power handling capability. The selection of RF cable is based on the main specifications that a particular application demands (cable specifications can be found in the manufacturer data sheet). Engineers have to analyze the real performance of RF cables for each application.
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