RF cables assemblies, important elements in many systems, are indispensable for delivering high-frequency signal interconnections—with no room for failure or mistakes.
They are considered crucial signal-routing components in numerous RF systems, even though they are frequently specified and added as an afterthought. For military applications, high-reliability cables’ strength and durability can determine the difference between life and death. In deep-space missions, like communications or surveillance satellites, cable malfunction is not an option. But military and aerospace are no longer the unique application areas for hi-rel cables and connectors.
More industrial and commercial users come to depend on long operating lifetimes from cables installed in such applications as communications systems and manufacturing equipment.
Selecting a hi-rel RF cables assembly can be essential to completing a system design, regardless of its final purpose (whether it’s for commercial, industrial, or military applications). But choosing the right cable goes beyond looking at some requirements and making a cable fit a set of specifications. It’s necessary to understand how reliability is defined for different applications. Once defined, one needs to determine how to achieve reliability with various types of RF cables assemblies and that it stands the test of time and whatever an application can throw at it.
What Constitutes Reliability?
Reliability is usually determined in terms of product failures and lifetimes in the form of a bathtub curve as a function of time, with three separate failure rates over a product’s lifetime. The initial is a period of decreasing failures, then followed by a period of continuous failures, with a third and last period of increasing failures during the wear-out stage of the product. High-reliability cables are produced for a minimum number of failures along the bathtub curve and lifetime of the cable assemblies so that the following system failures do not result from the failing interconnects.
Reliability refers to receiving the expected ranges of effectiveness from a cable assembly each time it’s utilized, without degradation or loss in performance for the application’s full lifetime. Failure of a cable assembly can be expected when it passes the mechanical or electrical, or environmental limits set for it, such as forming a flexible cable into a bend radius smaller than the recommended minimum. Another failure circumstance would be applying RF cable power levels higher than the rated maximum or operating the cable assembly at temperatures going above the specified operating temperature range.
The definition of reliability becomes more complicated when limits are established for performance degeneration that’s acceptable over time. A coaxial cable assembly’s efficiency can be defined by several different parameters, such as insertion loss, VSWR, and phase stability.
A cable’s reliability may be associated with keeping close control on just one or two performance parameters on a full set of parameters. The demanded tolerances for what describes a hi-rel cable assembly can vary from one application to another.
In conclusion, the reliability of a coaxial cable assembly is very much a function of an application and its operating environment.
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