SMA connector performance
SMA connectors are designed to have a constant, 50 ohm impedance across the connector. SMA connectors were originally designed and specified for operation up to 18 GHz, although some versions top out at 12.4 GHz and some are specified at 24 or 26.5 GHz. A higher upper frequency limit may require operation with higher return loss.
Generally, SMA connectors have higher reflection coefficients than other connectors up to 24 GHz. This is due to the difficulty of accurately securing the dielectric support, but despite this difficulty, some manufacturers have managed to overcome this problem properly and have been able to specify their connectors for 26.5GHz operation.
For flex cables, the frequency limit is usually determined by the cable, not the connector. This is because the cables accepted by SMA connectors are small, and their losses are naturally much greater than the losses of the connectors, especially at the frequencies they are likely to be used in.
SMA connector power rating
In some cases, the power rating of the SMA connector can be important. The key parameters that determine the average power handling capability of a mated coaxial connector is its ability to deliver high currents and maintain a moderate heat gain.
The heating effect is mainly caused by the contact resistance, which is a function of the contact surface area and the way the contact pads are held together. A critical area is the center contacts, which must form correctly and fit together nicely. The average power rating decreases with frequency because resistive losses increase with frequency.
