What is the difference between SMA, 3.5mm, 2.92mm, 2.4mm, and 1.85mm connectors?
Precision Connector Family
The progression from SMA to 1.85mm represents a systematic reduction in connector dimensions to extend the frequency range. Each step reduces the outer conductor diameter, raising the TE11 cutoff frequency. Simultaneously, tolerances become tighter (and costs higher) because the smaller dimensions require more precise machining to maintain 50 Ω impedance.
| Parameter | Semi-Rigid | Conformable | Flexible |
|---|---|---|---|
| Loss (dB/m at 10 GHz) | 0.8-2.5 | 1.0-3.0 | 1.5-5.0 |
| Phase Stability | Excellent | Good | Fair |
| Bend Radius | Fixed after forming | Hand-formable | Continuous flex OK |
| Shielding (dB) | >120 | >90 | >60-90 |
| Cost (relative) | 2-5x | 1.5-3x | 1x |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
Which should I use for general lab work?
SMA for below 18 GHz (lowest cost, widest availability). 3.5mm or 2.92mm for 18-40 GHz work. 2.4mm for 40-50 GHz. Match the connector to your highest operating frequency and use that connector throughout the measurement setup for consistency.
Can I adapt between families?
Yes, but each adapter adds loss (0.1-0.5 dB) and reflection (typically 15-25 dB return loss). Minimize the number of adapters in any measurement path. Between-family adapters (e.g., SMA to 2.4mm) require a thread change and are bulkier than within-family adapters.
What is the cost difference?
SMA connectors: $5-20 each. 3.5mm: $30-100. 2.92mm: $50-150. 2.4mm: $100-300. 1.85mm: $200-500. Cables and adapters scale similarly. The cost reflects the tighter machining tolerances required for higher-frequency connectors.