Why do connectors have frequency limits and what happens when I operate above the rated frequency?
Above-Cutoff Operation Effects
Below the TE11 cutoff frequency, a coaxial connector supports only one propagating mode (TEM). The connector geometry determines the impedance, loss, and reflection in a predictable, repeatable manner. Calibration can remove systematic errors, and measurements are reproducible within the connector's specification.
| 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
Frequently Asked Questions
What if I only need rough measurements?
For approximate measurements with 2-3 dB uncertainty, some engineers use SMA connectors to 30 GHz or Type N to 20 GHz. This is acceptable for troubleshooting or development testing but not for final characterization or specification verification.
How do I know if higher-order modes are present?
Symptoms include: rapidly varying S-parameters with frequency (ripple), large changes in measurement when rotating the connector, poor measurement repeatability (> 0.5 dB variation between connections), and unexpected resonant dips in S21.
What is the solution?
Use the correct connector for the frequency: 2.92mm for 26-40 GHz, 2.4mm for 40-50 GHz, 1.85mm for 50-67 GHz, and 1.0mm for 67-110 GHz. The increased cost of precision connectors is justified by reliable, repeatable measurements.