RF Coaxial Connector Overview
RF connectors define the frequency ceiling of any measurement system or assembly. Choosing the wrong connector adds insertion loss, reflection, and limits useful bandwidth. This guide covers the most common 50 Ω connectors used from DC to 110 GHz.
Connector Comparison Table
| Connector | Max Freq | Impedance | Mating Cycles | Typical IL at Max Freq |
|---|---|---|---|---|
| Type N | 18 GHz | 50 Ω | 500 | 0.3 dB |
| SMA | 18 GHz (26 GHz usable) | 50 Ω | 500 | 0.4 dB |
| 3.5 mm | 34 GHz | 50 Ω | 2,000 | 0.3 dB |
| 2.92 mm (K) | 46 GHz | 50 Ω | 2,000 | 0.4 dB |
| 2.4 mm | 65 GHz | 50 Ω | 2,000 | 0.5 dB |
| 1.85 mm (V) | 67 GHz | 50 Ω | 2,000 | 0.6 dB |
| 1.0 mm | 110 GHz | 50 Ω | 500 | 1.0 dB |
Mating Compatibility
| Connector | Compatible With | Frequency Limit When Mated |
|---|---|---|
| SMA | 3.5 mm (mechanical only) | 18 GHz (SMA limit) |
| 3.5 mm | SMA (with care), 2.92 mm | 34 GHz |
| 2.92 mm | 3.5 mm, SMA (with care) | 34 GHz when mated with 3.5 mm |
| 2.4 mm | 1.85 mm | 65 GHz |
| 1.85 mm | 2.4 mm | 65 GHz |
SMA Deep Dive
SMA (SubMiniature version A) is the most common RF connector. Despite its 18 GHz specification, it is widely used to 26 GHz in lab settings with careful torque (5 in-lb) and short cable sections. Key SMA pitfalls:
- Overtorquing damages the center pin dielectric
- Mixed SMA bodies from different vendors can mismate (different center pin diameters)
- Panel-mount SMA solder joints are a common source of VSWR spikes
Connector Effect on S-Parameters
Every connector adds a small reflection and insertion loss to S-parameter measurements. RF View can help characterize connector quality: measure a short connector-pair (male-male adapter or through calibration standard) and inspect S11 and S21 across frequency. A good SMA adapter should show:
- S11 < −25 dB below 10 GHz
- S21 > −0.1 dB below 10 GHz
Degraded connectors show resonance spikes in S11 and S21 at specific frequencies corresponding to connector dimensions.