RF Cable Basics: Types, Specifications, and Manufacturers

Radio frequency (RF) has long been used to carry electromagnetic (E-M) waves from a source to a destination. The medium between the source and the destination can be either air or a cable. An antenna is used to guide E-M waves through the air. An RF cable, on the other hand, is used to interface E-M waves between two systems or between a device under test (DUT) and test equipment.

For longer distances, RF cable isn’t ideal due to signal loss. Instead, antennas are preferred. Just as different antennas are used for different frequencies of operation, different cables are used for different radio frequencies.

RF cables are widely used for testing purposes, such as connecting a DUT to an RF signal generator, analyzer, spectrum analyzer, or power meter. Another common application is connecting one module to another within a system, such as an RF transceiver or a solid-state power amplifier (SSPA). This could involve connecting a reference oscillator output to the input of a local oscillator/synthesizer, or connecting the local oscillator output to the input of an up-conversion/down-conversion stage.

RF cables are primarily selected based on these three generic applications:

• Flexibility: Considering the system’s needs, whether semi-flexible, flexible, rigid, semi-rigid, or coaxial cable is most appropriate.
• Connector Type: Matching the connectors required for the connection points (e.g., SMA, N-type, TNC).
• Frequency of Operation: Choosing a cable suitable for the intended frequency range.

Beyond these generic parameters, insertion loss and return loss are crucial specifications.

Insertion loss is the amount of RF signal lost as it passes through the cable. For example, if the insertion loss is specified as 0.5dB at a certain frequency, and the input power is 5dBm, then the output power will be approximately 4.5dBm.

Return loss should ideally be as high as possible. It measures how much power is reflected back from the cable versus how much passes through.

Typically, RF cable manufacturers provide tables and graphs showing insertion loss and return loss across a frequency range. This allows users to choose the most suitable cable for their specific application.

Specifications of RF Cables

Here’s a summary of key specifications to consider when selecting an RF cable:

• Connector type
• Cable type
• Frequency of operation
• Insertion loss (or attenuation) per meter
• Return loss
• Impedance (50 Ohm, 75 Ohm, 95 Ohm)
• Dielectric material used
• Signal delay
• Operating voltage
• Military or non-military use

Figure: Connectorized RF cable and open-ended cable used for debugging during RF component assembly and RF testing.

The RF cable shown in the figure is a flexible type. The connectorized cable has an SMA connector on one side and a TNC connector on the other.

When purchasing a cable, in addition to the specifications listed above, you may need to specify the class it falls under, such as RG or M (military) application.

RF Cable Types (RG)

Here are a few common RF cable types. The “R” stands for Radio frequency, and “G” stands for Government. The numbers (e.g., 8, 11) are numbers assigned by the government for approval, and “/U” signifies a universal specification.

• RG 8A/U: 50 ohm impedance cable
• RG 11A/U: 75 ohm impedance cable
• RG 22B/U: 95 ohm impedance cable

Popular RF Cable Manufacturers

Here are some well-known manufacturers of RF cables:

• HUBER+SUHNER: www.hubersuhner.com/
• Cobham: https://www.cobham.com/
• W. L. Gore & Associates, Inc.: https://www.gore.com/
• HIRAKAWA HEWTECH Corporation, Japan: www.hewtech.co.jp/e/
• amphenolrf: www.amphenolrf.com
• hollandelectronics: www.hollandelectronics.com
• Carlisle Interconnect Technologies: www.tensolite.com
• UK.RS-ONLINE: https://uk.rs-online.com/web/
• Zcomm: https://www.zcomm.com/
• Radiall: (Global leader in RF coaxial connectors and cable assemblies) www.radiall.com
• Lighthorse Technologies, Inc.: (Cable assembly manufacturer) www.rfconnector.com