Published on 10/13/2026
A technician bends a 0.141 in semi-rigid cable around a pen, straightens it, and bends it again to fix the angle. The signal still passes, but return loss at 18 GHz has quietly gotten worse. The outer conductor wrinkled or cracked at the second bend and nothing on the surface says so.
Short answer: yes, semi-rigid coax can be bent, but treat it as formed once, not flexed. The minimum bend radius is about 6.35 mm (0.25 in) for 0.141 in cable and about 3 mm for 0.085 in cable, bent with a proper tool and with straight lengths kept at each connector.
This guide gives the radii, the forming steps and the mistakes that cause hidden damage.
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Bend radius is measured to the inside of the bend. Values below are typical for tin- or copper-jacketed solid-outer semi-rigid cable. Always check the datasheet for your exact cable, because the specified radius depends on the maker.
| Cable | Size | Typical minimum radius | Comment |
|---|---|---|---|
| RG405 / 0.086 in | 2.2 mm OD | About 3.2 mm (0.125 in) | Common for SMA assemblies |
| RG402 / 0.141 in | 3.6 mm OD | About 6.35 mm (0.25 in) | Most common semi-rigid |
| 0.047 in | 1.2 mm OD | About 1.6 mm (0.0625 in) | Very fine, use a small tool |
| 0.250 in | 6.4 mm OD | About 12 to 19 mm | Check datasheet; needs a press tool |
Key idea: As a rule of thumb, keep the inside bend radius at 3 times the outer diameter or more, and never below the datasheet minimum.
Rule 01
Use a bending tool or jig
Hand bending by finger or pliers kinks the cable. A forming jig or bending spring keeps a round cross-section.
Rule 02
Keep straight lengths at connectors
Leave at least 2 to 3 times the connector coupling length straight at each end, usually 10 to 12 mm, so the connector does not stress.
Rule 03
Bend once, in the right place
Repeated bending work-hardens the copper outer conductor and can crack it.
Rule 04
Account for spring-back
Bend slightly past the target angle. A 90 degree bend springs back a few degrees.
Rule 05
Measure before cutting
Bends add length compensation. Formed cable should be cut after the bends are planned.
Order it already formed
Custom semi-rigid assemblies can be formed to your drawing and swept on a VNA for VSWR and insertion loss before shipment.
Talk to an Engineer| Type | Bending | Typical use |
|---|---|---|
| Semi-rigid (copper or tin outer) | Formed once, then fixed | Inside instruments, between modules |
| Conformable (hand-formable) | Can be re-formed a few times by hand | Prototyping, lab |
| Flexible (RG316, LMR) | Flexes continuously | Cable runs, moving parts |
If the path changes often, use conformable or flexible cable. See our RF cable selection and semi-rigid guides on this blog.
Damage that is hard to see
After forming
Can you bend semi-rigid coax?
Yes. Form it once with a proper tool and keep to the minimum bend radius. Do not flex it repeatedly.
What is the minimum bend radius of RG402?
About 6.35 mm (0.25 in) for the 0.141 in size, measured at the inside of the bend.
Can I straighten and rebend semi-rigid cable?
Not without risk. The outer conductor work-hardens and can crack, which raises VSWR.
How close to the connector can I bend?
Leave about 10 to 12 mm of straight cable at each connector for 0.141 in cable.
What is the difference between semi-rigid and conformable?
Conformable has a flexible outer layer that can be re-formed by hand. Semi-rigid is formed once.
Does bending semi-rigid cable change its loss?
A clean bend at the minimum radius has no measurable effect. A kinked bend raises VSWR and loss.
Semi-rigid cable is meant to be shaped, but only once and only above the minimum radius. If you expect to rework the shape, use conformable cable, or order the part pre-formed.
SigmaRF builds semi-rigid and flexible assemblies in India (Vadodara) and the USA (Cleveland area), VNA-swept before shipment, with lead times as short as 2 days.
Need a formed semi-rigid assembly?
Send a drawing or a sample.
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