Which RF connector should you use?
Choose an RF connector by frequency range, power, size and repeatability. SMA is the general-purpose choice to about 18 GHz (some precision versions higher); Type N handles higher power to about 11–18 GHz; BNC suits low-frequency test; precision 3.5 mm, 2.92 mm, 2.4 mm, 1.85 mm and 1.0 mm connectors extend to about 34, 40, 50, 67 and 110 GHz respectively.
How do common connectors compare?
| Connector | Typical max frequency | Notes |
|---|---|---|
| BNC | ~4 GHz (often used ≤ 1 GHz) | Bayonet; 50 Ω and 75 Ω versions |
| TNC | ~11 GHz | Threaded BNC |
| Type N | 11–18 GHz | Rugged, higher power; 50 and 75 Ω versions not intermateable |
| SMA | 18 GHz (precision to ~26.5) | Most common on boards and modules |
| 3.5 mm | 34 GHz | Air dielectric, mates with SMA |
| 2.92 mm | 40 GHz | Mates with SMA and 3.5 mm |
| 2.4 mm / 1.85 mm | 50 / 67 GHz | Mate with each other, not SMA |
| 1.0 mm | 110 GHz | mmWave test |
| U.FL / MHF / IPEX | ~6 GHz | Miniature board-to-cable, limited mating cycles |
Limits vary by manufacturer; use datasheet values.
How should precision connectors be handled?
- Use a calibrated torque wrench (SMA commonly 5 in-lb / 0.56 N·m for steel; 3.5/2.92/2.4 mm commonly 8 in-lb / 0.9 N·m). Check the manufacturer’s values.
- Turn the nut, not the body, to avoid wearing the center pin.
- Inspect and gauge pin depth; clean with isopropyl alcohol.
- Use connector savers on instruments.
What about board launches?
The transition from connector to PCB trace is often the worst discontinuity in a system above a few GHz. End-launch connectors with optimized pad and ground-via patterns, verified by EM simulation and TDR, keep return loss acceptable.
Frequently asked questions
Can SMA mate with 2.92 mm?
Yes, mechanically compatible, though an SMA in the pair limits performance and can damage precision connectors if out of spec.
Why not use SMA at 40 GHz?
Its dielectric-filled design supports higher-order modes above about 18–26 GHz.
Are 75 Ω N connectors compatible with 50 Ω?
No; the center-pin sizes differ and mating can cause damage.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Understanding the Fundamental Principles of Vector Network Analysis (Application Note 1287-1)”. Keysight Technologies. application note.