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What Is SMA Connector?

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SMA connectors are widely used as semi-precise, ultra-miniature RF and microwave connectors, especially for RF connections within electronic systems with frequencies up to 18 GHz and beyond.

The SMA connector is available in various forms, male, female, straight, right angle, bulkhead mount and many more features that make it suitable for most requirements. Its ultra-compact size allows it to be used even in relatively small electronic devices.

Although now well established, the use of SMA connectors is likely to expand as many new RF systems see their operating frequencies extend well into the microwave region.

Although SMA connectors look very similar to the standard domestic connectors used for domestic satellite TV and other similar applications. These household connectors are called F-type coaxial connectors and they have an impedance of 75 Ω. They have a different diameter and cannot be matched to SMA connectors - they require a special adapter and then there is an impedance mismatch.

SMA connector basics

The SMA connector is an ultra-small coaxial cable connector. It finds many applications for providing connectivity for RF components within devices that require a coaxial connection. It is commonly used to provide RF connectivity between boards and many microwave components (including filters, attenuators, mixers and oscillators) use SMA connectors.

The connector has a threaded external connector interface that has a hexagonal shape and can be tightened with a spanner. A special torque spanner can be used to tighten it to the correct tightness so that a good connection can be made without over-tightening. The torque required is typically 8-inch pounds.

SMA Connector

SMA coaxial RF connectors were originally designed by Bendix Scintilla Corporation and Omni-Spectra Corporation in the 1960s. The first SMA connectors were designed for 141 semi-rigid coaxial cables. The original SMA connector could be called the smallest connector because the centre of the coaxial cable formed the centre pin of the connection, thus eliminating the need for a transition between the centre conductor of the coaxial cable and the centre pin of the special connector. It also has the advantage that the cable dielectric can be brought directly to the interface without leaving an air gap. The disadvantage of the connector is that only a limited number of connecting/disconnect cycles can be made. However, this is unlikely to be a problem for applications using semi-rigid coaxial cables, as the device is usually secured after initial assembly.

However, its use was extended to other flexible cables and complete connectors with a central pin were introduced. These connectors are manufactured to a high standard and allow more connect/disconnect cycles to be performed. 

SMA connector performance

SMA connectors are designed to have a constant 50 Ohm impedance at the connector. SMA connectors were originally designed and specified for operation up to 18 GHz, although some versions are available up to 12.4 GHz and some up to 24 or 26.5 GHz. higher frequency limits may require operation with higher return losses.

The actual specification of a given connector depends very much on the manufacturer and type - there are several different categories of quality/performance available. It is always best to check connector specifications carefully