What makes a cable phase stable?
A phase stable cable holds its electrical phase steady when it is bent, flexed, or heated. Manufacturers spec this two ways: phase change versus flexure, in degrees at a set frequency and mandrel size, and phase change versus temperature, in parts per million. Lower numbers mean less error in phase-matched systems. Both matter, and they rarely rank cables the same way.
Phase versus flexure: the number buyers compare first
Phase versus flexure tells you how much a cable's phase shifts when you wrap it around a mandrel. If your cables move (test benches, antenna ranges, anything on a gimbal), this is the spec that shows up in your data.
All values below come from the Micro-Coax UTiFLEX catalog and are measured with the cable wrapped once around a 3 inch mandrel.
| Cable | Family | Center conductor | Max freq | Phase vs. flexure @ 10 GHz | @ 18 GHz |
|---|---|---|---|---|---|
| UFC092D | Low-Loss | Solid | 70 GHz | <0.5° | <0.5° |
| UFA147B | Low-Loss | Stranded | 40 GHz | 1° | 2° |
| UFA210B | Low-Loss | Stranded | 26.5 GHz | 2° | 3° |
| UFA147A | Low-Loss | Solid | 40 GHz | 2° | 4° |
| UFA210A | Low-Loss | Solid | 26.5 GHz | 2° | 4° |
| UFB197C | Ultra-Low-Loss | Stranded | 26.5 GHz | 2° | 3° |
| UFB293C | Ultra-Low-Loss | Stranded | 18 GHz | 2° | 3° |
| UFB142A | Ultra-Low-Loss | Solid | 40 GHz | 2° | 5° |
| UFB205A | Ultra-Low-Loss | Solid | 26.5 GHz | 4° | 7° |
| MKR300C | Test cable | Stranded | 26.5 GHz | 2° | 3° |
Two patterns stand out. First, the UFC092D is the tightest in the catalog at under half a degree, and it runs to 70 GHz. Second, stranded center conductors generally hold phase better under flexure than solid ones. Compare the UFA147B (stranded) to the UFA147A (solid) at the same diameter: 2° versus 4° at 18 GHz. Solid conductors give you lower loss instead, so it's a tradeoff.
Phase versus temperature
Every PTFE cable has a bump in its phase curve near room temperature, where the dielectric changes state. It's the same physics across the whole product line, but the size of the swing depends on the cable.
Reading the catalog's typical curves:
| Temperature | Low-Loss and Miniature (approx. ppm) | Ultra-Low-Loss and Ultra-Light (approx. ppm) |
|---|---|---|
| -60°C | ~1,600 | ~500 |
| 0°C | ~1,200 | ~580 |
| 20 to 30°C | ~0 (dips slightly negative) | ~0 |
| 100°C | ~250 | ~620 |
The takeaway: if your system sees big cold swings, the ultra-low-loss dielectric keeps the excursion far smaller at low temperatures. The low-loss family drifts more in the cold but less at the hot end.
These are approximate readings from the published typical curves, not guaranteed limits. Confirm exact figures for your application with our team.
How to pick a phase stable cable
- Moving cables, test lab: UFA210B or MKR300C. Stranded conductors and long flex life (the MKR300C is rated for 150,000 flexes).
- Tightest phase under flexure: UFC092D.
- Lowest loss with good phase behavior: UFB197C or UFB293C.
- Big temperature swings: ultra-low-loss or ultra-light. Check the curve above.
- Weight-critical or space: ultra-light (MCJ/UFJ series) or the TVAC assemblies, which use low-outgassing materials and vented connectors.
Need matched assemblies? UTiFLEX cables can be built phase matched. For absolute phase matching, ask about the "AM" code.
Why buyers stay with UTiFLEX
CDI has been a Micro-Coax franchise distributor for over 25 years. For a buyer, that history mostly means consistency: the same product family, the same specs, and the same team behind the quote year after year.
UTiFLEX assemblies are built in Pottstown, PA, so there's no overseas build and no tariff surprise on the cable itself. Every assembly is tested for insertion loss and SWR and ships with its own test certificate.
Phase stable cable FAQ
What is a good phase stability spec for a microwave cable?
It depends on frequency and how much the cable moves. For flexing applications, 1° to 3° at 10 GHz is strong. For fixed installs, temperature stability usually matters more.
Is a phase stable cable the same as a phase matched cable?
No. Phase stable describes how much phase changes under stress. Phase matched means a set of cables is built to the same electrical length so they line up with each other. You often want both.
What causes low phase drift in a cable?
Mostly the dielectric and the center conductor. A low-density PTFE dielectric has low thermal expansion, and stranded conductors tolerate bending better.
Can I get a custom length or connector?
Yes. Assemblies are built to your length and connector, with SMA, SMK, 2.4 mm, precision N, TNC, and more available. Request a quote and we'll match it to your spec.
Request a quote: send your frequency range, connector types, length, and environment to sales@cdiweb.com or call 1-800-777-7334.
