Published on 7/27/2026 • Updated on 7/27/2026
At 6 GHz, an RF connector is a mechanical part. At 40 GHz, it is a precision instrument. The difference between an SMA that costs a few dollars and a 1.85 mm that costs several hundred is not markup. It is the tolerance you need to hold on an internal air gap that gets smaller and more critical the higher in frequency you go. Get that wrong and your measurement is wrong, your test port wears out early, and expensive parts get damaged the first time an incompatible connector is forced onto them.
This is a working guide to the four connectors you meet above 18 GHz: standard SMA, 2.92 mm (K), 2.4 mm, and 1.85 mm (V). What each one is for, which ones mate safely with which, and how to pick between them without over-spending or under-specifying.
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A connector is part of the transmission line. At any frequency, its job is to hold 50 ohms across the mating interface with a controlled internal geometry. The difference at microwave and millimeter-wave frequencies is that the wavelength gets shorter, which means the internal dimensions that define impedance get proportionally more critical.
At 6 GHz, the wavelength in air is about 50 mm. A tenth-of-a-millimeter geometric error inside a connector is negligible. At 40 GHz, the wavelength is 7.5 mm, and the same error is now a substantial fraction of the internal dimensions. Reflections rise, VSWR degrades, and repeatability suffers. This is why precision connectors have smaller diameters (the number in the name is the outer conductor inner diameter in mm) and tighter tolerances than SMA.
| Connector | Also Called | Max Frequency | Mates With | Typical Use |
|---|---|---|---|---|
| SMA | Standard | 18 GHz (26.5 precision) | SMA, 3.5 mm, 2.92 mm | General RF, Wi-Fi, GPS, cellular |
| 2.92 mm | K Connector | 40 GHz | SMA, 3.5 mm, 2.92 mm | Microwave test, radar, sat-com |
| 2.4 mm | (no letter) | 50 GHz | 2.4 mm and 1.85 mm only | Precision measurement, calibration |
| 1.85 mm | V Connector | 67 GHz | 1.85 mm and 2.4 mm only | mmWave, 5G, radar, aerospace |
The K and V designations come from the original Wiltron (now Anritsu) naming: K for the K-band coverage of the 2.92 mm, V for the V-band coverage of the 1.85 mm. You will hear both names used interchangeably in the field.
SMA stands for SubMiniature Version A. It is by far the most common RF connector in the world, and if you have worked with Wi-Fi routers, GPS modules, SDR hardware, or laboratory test equipment, you have used one. Threaded, 50 ohms, PTFE dielectric, and specified from DC to 18 GHz in standard commercial form. Precision SMA parts extend that to about 26.5 GHz, but not everything called "SMA" holds spec that high.
Strengths
Limitations
Practical torque: 5 in-lb (0.56 Nm) for standard commercial SMA, 8 in-lb (0.9 Nm) for precision SMA and 3.5 mm.
The 2.92 mm connector was developed to do what SMA cannot: hold spec cleanly to 40 GHz. Outer thread pitch matches SMA, so it can physically mate with SMA and 3.5 mm connectors, which is why it became the go-to microwave test connector in labs that also use lower-frequency gear.
This is the connector engineers reach for when they need to test something above 18 GHz but still want to use their existing SMA cables and calibration standards. Nearly every vector network analyzer test cable rated to 40 GHz is 2.92 mm.
Typical uses: microwave and mmWave test benches, VNA test cables to 40 GHz, radar signal generators, satellite ground segment testing, high-frequency signal generators and spectrum analyzers.
Practical torque: 8 in-lb (0.9 Nm).
The 2.4 mm connector exists for one reason: it will not physically mate with SMA or 3.5 mm. That is a feature, not a limitation. Above 40 GHz, an accidental mating with a worn SMA can destroy a precision interface in one motion. The 2.4 mm design deliberately blocks that.
Electrically, it is the step up from 2.92 mm. Tighter tolerances, better repeatability, better return loss, and 50 GHz coverage. It mates with 2.4 mm and (with proper hardware) with 1.85 mm. It does not mate with anything below 2.4 mm in size.
Typical uses: precision RF measurement, calibration standards, high-frequency instrumentation, on-wafer semiconductor test, R&D above 40 GHz.
Practical torque: 8 in-lb (0.9 Nm).
Above 50 GHz, you are in millimeter-wave territory: 5G FR2, automotive radar, satellite links, radio astronomy, aerospace research. The 1.85 mm connector is what you use to get there. Rated to 67 GHz in standard form, with premium versions going higher.
The internal air dielectric and precision-machined center pin make these connectors expensive and sensitive. Contamination that would not affect an SMA can change 1.85 mm return loss noticeably. Handling discipline is not optional at this level.
1.85 mm mates with 2.4 mm (they share the same interface geometry), which is useful when a system needs to cover 50 GHz and 67 GHz measurement points without swapping hardware. It does not mate with anything larger.
Typical uses: mmWave R&D, 5G FR2 test, automotive radar (76 to 81 GHz), aerospace and defense mmWave, satellite communications, advanced VNA calibration.
Practical torque: 8 in-lb (0.9 Nm).
Two connectors sit at the edges of this family and are worth naming.
3.5 mm
A precision SMA-compatible connector rated to 26.5 GHz. Physically mates with SMA and 2.92 mm. Sits between precision SMA and 2.92 mm in cost and performance. Common on older test equipment and cal kits.
Use if: your work sits at or under 26.5 GHz and you want measurement-grade repeatability without stepping up to 2.92 mm.
1.0 mm
Reserved for measurements up to 110 GHz. Extraordinarily small internal dimensions, extraordinarily expensive, and used almost exclusively in metrology labs and D-band and W-band research.
Use if: you are doing research above 67 GHz. Most engineers will never touch one.
Precision Cable Assemblies to 40 GHz and Beyond
SigmaRF builds tested microwave assemblies terminated with SMA, precision SMA, 3.5 mm, 2.92 mm, 2.4 mm and 1.85 mm connectors on semi-rigid and phase-stable flexible cable. Each assembly is individually swept for VSWR and insertion loss before it ships.
Get a Custom Assembly →Green means safe, amber means possible but shortens the life of the precision part, red means do not do it.
| Mate | SMA | 3.5 mm | 2.92 mm | 2.4 mm | 1.85 mm |
|---|---|---|---|---|---|
| SMA | ✓ | ⚠ | ⚠ | ✗ | ✗ |
| 3.5 mm | ⚠ | ✓ | ✓ | ✗ | ✗ |
| 2.92 mm | ⚠ | ✓ | ✓ | ✗ | ✗ |
| 2.4 mm | ✗ | ✗ | ✗ | ✓ | ✓ |
| 1.85 mm | ✗ | ✗ | ✗ | ✓ | ✓ |
✓ Green: safe, same-family mating.
⚠ Amber: mechanically possible, electrically acceptable, but the precision part loses life with every cycle. Use a test-port saver.
✗ Red: do not attempt. Forcing incompatible pin diameters destroys both connectors instantly.
| If Your Application Is... | Recommended Connector |
|---|---|
| Wi-Fi, cellular, GPS, general RF up to 6 GHz | Standard SMA |
| Bench test and R&D up to 18 GHz | Precision SMA or 3.5 mm |
| Precision test up to 26.5 GHz | 3.5 mm |
| Microwave test up to 40 GHz | 2.92 mm (K) |
| Precision measurement up to 50 GHz | 2.4 mm |
| mmWave up to 67 GHz (5G FR2, automotive radar) | 1.85 mm (V) |
| Research above 67 GHz | 1.0 mm |
Precision microwave connectors will not forgive sloppy handling the way SMA does. A few habits worth keeping:
What is the difference between SMA and 2.92 mm connectors?
SMA is rated to 18 GHz (26.5 GHz for precision versions) and is a commercial-grade connector. The 2.92 mm connector is a precision microwave connector rated to 40 GHz. They can physically mate because they share the same thread and outer geometry, but a 2.92 mm has tighter internal tolerances designed for accurate measurement at microwave frequencies.
Can I mate a 2.4 mm connector with an SMA?
No. The 2.4 mm connector is intentionally not compatible with SMA. The internal pin geometry is different, and forcing them together will destroy both connectors instantly. Use a purpose-built adapter (SMA to 2.4 mm) if you need to bridge between them.
What is the K connector?
"K connector" is another name for the 2.92 mm connector. The name comes from Wiltron (now Anritsu), which developed it to cover the K microwave band. Engineers use both names interchangeably.
What is the V connector?
"V connector" is another name for the 1.85 mm connector. Also from Wiltron/Anritsu, named for its coverage of the V microwave band. Rated to 67 GHz and mates with 2.4 mm connectors.
Do 2.4 mm and 1.85 mm connectors mate with each other?
Yes. They share the same interface geometry, so a 2.4 mm mates cleanly with a 1.85 mm. This is deliberate: it lets a lab cover 50 GHz and 67 GHz work without swapping connector families.
What torque should I use on precision RF connectors?
Standard SMA: 5 in-lb (0.56 Nm). Precision SMA, 3.5 mm, 2.92 mm, 2.4 mm and 1.85 mm all use 8 in-lb (0.9 Nm). Always use a calibrated torque wrench. Hand-tight is not tight enough, and hand-tight from a strong installer is too tight.
Which connector do I need for 5G FR2 (mmWave)?
5G FR2 covers 24 to 52 GHz. For 24 to 40 GHz test work, 2.92 mm is standard. For work up to 50 GHz, use 2.4 mm. For the upper edge of FR2 and future extensions, 1.85 mm gives you headroom to 67 GHz.
Are precision RF connectors worth the cost?
For work above 18 GHz, yes. The extra cost buys you tighter tolerances, better VSWR, better repeatability, and longer mating life. For general RF at or below 6 GHz, commercial SMA is sufficient and the precision uplift buys you very little.
How long do precision RF connectors last?
Commercial SMA: a few hundred mating cycles. Precision SMA and 3.5 mm: 500 to 3,000 cycles depending on grade. 2.92 mm: 3,000 to 5,000 cycles. 2.4 mm and 1.85 mm: 5,000 cycles or more with proper handling. Cross-family mating (like SMA into 2.92 mm) shortens the life of the precision part significantly.
Pick by frequency first. SMA for anything at or below 18 GHz that does not need precision measurement. 3.5 mm or 2.92 mm when you need SMA compatibility with better microwave performance. 2.4 mm for precision work to 50 GHz. 1.85 mm for millimeter-wave to 67 GHz. Above that, 1.0 mm.
Then respect the hardware. Torque with a wrench. Inspect before mating. Do not force incompatible parts together. Use test-port savers on instruments. Cap unused connectors and clean them properly when they get dirty. Get those habits right and a good precision connector will outlast the instrument it is attached to.
Microwave and mmWave Cable Assemblies from SigmaRF
Tested cable assemblies terminated with SMA, precision SMA, 3.5 mm, 2.92 mm, 2.4 mm and 1.85 mm connectors on semi-rigid, conformable, and phase-stable flexible cable. Each assembly is individually swept for VSWR and insertion loss across its rated band before it ships.
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