Published on 10/13/2026
An engineer routes an RG316 jumper around a heat sink inside a compact radio. The cable makes a hard 90 degree turn only 8 mm from the SMA connector. Day one, the VSWR is 1.35:1. After thermal cycling it creeps to 1.9:1, and the return loss notch moves with the cable when you touch it.
Bend radius is the least glamorous cable spec and the most common cause of hidden RF failures. A bend that is too tight deforms the dielectric, shifts the shield braid, and changes the characteristic impedance at that spot, creating a small reflection that you cannot see by eye.
This guide gives practical bend radius rules with real numbers for the cables we build most, explains static versus dynamic bending, and shows how to route cable near a connector. For cable selection see our RF coaxial cable selection guide.
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Minimum bend radius is measured to the inside of the cable, not the centerline, and is expressed as a multiple of the outer diameter (OD). The commonly used rule for flexible braided coax is:
| Cable | Typical OD | Static bend (10x) | Dynamic bend (20x) |
|---|---|---|---|
| RG174 | 2.8 mm | 28 mm | 56 mm |
| RG316 | 2.5 mm | 25 mm | 50 mm |
| RG58 | 4.95 mm | 50 mm | 99 mm |
| RG142 | 4.95 mm | 50 mm | 99 mm |
| RG213 | 10.3 mm | 103 mm | 206 mm |
| Low-loss 400 series | 10.3 mm | 103 mm | 206 mm |
| Failure | Mechanism | What you see |
|---|---|---|
| Dielectric deformation | Core is flattened or off-center | Impedance bump, VSWR spike |
| Braid displacement | Shield opens at the outer side of the bend | Shielding loss, leakage, noise pickup |
| Center conductor offset | Conductor migrates through soft dielectric | Intermittent loss, phase jumps |
| Jacket cracking | Cold or UV-aged jacket | Moisture ingress, corrosion |
| Kink | Bend radius below limit, cable collapses | Permanent damage, replace the cable |
A kinked cable is not repairable. The kink may pass a continuity test and still produce a reflection large enough to fail a return loss limit at 6 GHz and above.
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Custom AssembliesStep 01
Start the bend away from the connector
Leave a straight run of at least 25 mm (about 1 in) behind the connector before any bend. The connector transition is already the most sensitive part of the cable.
Step 02
Support the cable
Clip or tie the cable within 50 mm of each end so weight and vibration do not load the connector. See our strain relief article for boots and clamps.
Step 03
Use a smooth sweep
Route in large arcs. Where space forces a tight turn, use a right-angle connector or an adapter instead of bending the cable.
Step 04
Keep away from sharp edges and heat
PTFE tolerates high temperature, PVC jackets do not. Keep cable off heat sinks and sheet metal edges.
Step 05
Avoid twisting
Twisting while bending adds stress. Lay the cable in place without torque on the connectors.
If the layout forces a small radius, choose the cable for the job instead of forcing the one you have. Thin RG316 and RG174 bend easily but have higher loss. Semi-rigid hand-formable cable can be formed to a tight, repeatable shape once, and it keeps its shape and its shielding at 100 percent. Right-angle connectors move the bend into a rigid part. See our semi-rigid cable guides for forming practice.
Right-angle connectorsHand-formable cableThinner cableSpiral coil assembliesFlexible low-loss cableBoard-edge launch
What is the minimum bend radius for coax cable?
For flexible braided coax, use 10 times the outer diameter for a fixed bend and 20 times for repeated flexing. Check the datasheet for the exact cable.
What is the minimum bend radius of RG316?
With an OD of about 2.5 mm, a conservative static radius is 25 mm and a dynamic radius is 50 mm. Some datasheets allow tighter one-time bends, so confirm for your cable.
What is the bend radius of RG58?
RG58 has an OD of about 4.95 mm, so plan on about 50 mm static and 99 mm dynamic.
Can you bend coax cable at a right angle?
Not as a sharp corner. Use a smooth sweep of at least 10 times the OD, or use a right-angle connector to turn the corner.
Does bending coax cable affect signal?
Yes, a bend below the limit changes impedance locally, which raises VSWR and can add loss and phase error. Gentle bends have negligible effect.
How close to the connector can I bend a cable?
Leave a straight section of at least 25 mm (1 in) behind the connector when possible, and clamp the cable within 50 mm.
How do I know if a coax cable is kinked?
Look for a visible flat spot or crease, and check return loss. A kink shows as a reflection at a fixed distance in a time-domain or distance-to-fault trace.
Is bend radius the same for static and dynamic use?
No. Dynamic bending needs about double the radius of a static bend because repeated flexing fatigues the braid and conductor.
Bend radius is a design input, not an afterthought. Use 10 times OD for a one-time static bend and 20 times for flex, start bends away from the connector, support the cable, and use a right-angle connector when space runs out.
SigmaRF builds assemblies in RG316, RG174, RG58, RG142, semi-rigid and semi-flexible cable, and every assembly is VNA-swept for VSWR and insertion loss before shipment, 100 MHz to 40 GHz. If your enclosure forces a tight route, send us the drawing and our engineers in Vadodara and the Cleveland area will propose a cable and connector combination that fits. Lead times start at 2 days.
Tight layout? Get a cable that fits.
Send your routing drawing and we will propose the cable and connector combination.
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