RF Cable & Connector Notes: Loss, Phase Stability and Power

Attenuation versus frequency and diameter

Cable loss rises with frequency and falls with conductor diameter, so there is always a trade between flexibility and attenuation. Loss is quoted per unit length at a given frequency; for long runs or high bands, low-loss constructions and larger diameters quickly pay off. Always check loss at your highest operating frequency, not just at a low reference.

Phase stability and flexibility

For measurement and phased systems, phase-stable cables hold their electrical length steady as they are flexed and as temperature changes, preserving measurement accuracy and channel-to-channel matching. General-purpose flexible cables are fine where absolute phase does not matter. Decide whether you need phase stability before choosing, since it strongly affects cable construction and price.

Power handling and connector families

High-power or high-temperature service needs cables and connectors rated for the power and the environment, with attention to average and peak power and to voltage standoff. Connector families are band-limited: larger types suit lower frequencies and higher power, while precision types extend into the millimeter-wave bands. Mating-cycle life, coupling mechanism and environmental sealing matter for field and repeated-use applications.

What to specify

Give the frequency range, maximum acceptable loss or cable length, whether phase stability is required, average and peak power, the connector types and gender at each end, and the environment (temperature, flexure, outdoor or armored needs). That is enough to define a suitable standard assembly.

Frequently asked questions

Which connector family should I use?

Match the connector to your highest frequency and power. Larger threaded types suit lower bands and higher power; precision types reach into the millimeter-wave bands. Also consider mating cycles and environmental sealing.

Do I need a phase-stable cable?

Only if absolute phase or channel matching matters — for measurement setups and phased systems. For general signal transfer, a standard flexible low-loss cable is sufficient and more economical.

How do I estimate cable loss?

Use the loss per unit length at your highest operating frequency and multiply by the run length, then add connector losses. Check the figure at the top of your band, where loss is greatest.

When do I need armored or ruggedized assemblies?

For field use, frequent handling, or harsh environments where crushing, abrasion or repeated flexing would damage a standard lab cable.