What is the difference between semi-rigid, conformable, and flexible coaxial cable and when do I use each?
Coaxial Cable Type Comparison
The mechanical structure of the outer conductor determines the cable's flexibility, shielding, loss, and phase stability. These properties trade off against each other, and no single cable type optimizes all parameters. Understanding the tradeoffs enables the correct selection for each application.
| Parameter | Semi-Rigid | Conformable | Flexible |
|---|---|---|---|
| Loss (dB/m at 10 GHz) | 0.8-2.5 | 1.0-3.0 | 1.5-5.0 |
| Phase Stability | Excellent | Good | Fair |
| Bend Radius | Fixed after forming | Hand-formable | Continuous flex OK |
| Shielding (dB) | >120 | >90 | >60-90 |
| Cost (relative) | 2-5x | 1.5-3x | 1x |
Frequently Asked Questions
What about phase stability?
Semi-rigid: <2°/GHz variation over temperature. Conformable: 5-10°/GHz. Flexible: 10-30°/GHz. For phase-critical applications (phased arrays, interferometers), semi-rigid is essential. For general interconnect, flexible is adequate.
Which lasts longest?
Semi-rigid has essentially infinite flex life because it is not flexed. Conformable can be reshaped 3-5 times before fatigue. Flexible test cables are rated for 5,000-100,000 flex cycles depending on quality. Budget cables may fail in <1,000 cycles.
What about cost?
Semi-rigid is least expensive per foot but requires precision bending and skilled assembly. Conformable is moderately priced. High-quality flexible test cables are the most expensive due to the advanced materials and construction needed for repeatability and flex life.