SMA
Understanding SMA Connectors
SMA connectors were developed in the 1960s and have become the universal interface for RF connections below 18 GHz. Their small size, reliable threaded coupling, and good electrical performance make them the default choice for laboratory, production, and field applications.
SMA Variants
- Standard SMA: DC-18 GHz, stainless steel body. The original and most common version.
- 3.5mm precision: Compatible with SMA but with tighter tolerances. DC-34 GHz. Used for calibration and precision measurement.
- 2.92mm (K connector): Mates with SMA. DC-40 GHz. Used for Ka-band work.
- SSMA: Smaller version. Less common.
Key Specifications
- Frequency range: DC to 18 GHz (standard), to 26.5 GHz (extended)
- Impedance: 50 ohms
- VSWR: < 1.10 at DC, < 1.30 at 18 GHz (typical)
- Insertion loss: < 0.1 dB per connection
- Power handling: 100-500 watts depending on frequency
Thread: 1/4-36 UNS
Center conductor: 0.036 in (0.9 mm)
Dielectric: 0.121 in (3.08 mm) outer
Torque: 5 in-lb (0.56 N-m)
Mating cycles: 500+ minimum
Frequently Asked Questions
What is an SMA connector?
SMA is the most common RF connector for frequencies up to 18 GHz. It uses a threaded coupling for reliable connection, maintains 50-ohm impedance, and is available in bulkhead, edge-launch, cable, and PCB mount configurations.
What is the frequency limit of SMA?
Standard SMA is rated to 18 GHz. Extended-frequency versions work to 26.5 GHz. For higher frequencies, use 2.92mm (40 GHz), 2.4mm (50 GHz), 1.85mm (67 GHz), or 1.0mm (110 GHz) connectors. SMA mates with 3.5mm and 2.92mm connectors.
How tight should SMA connections be?
SMA connections should be torqued to 5 inch-pounds (0.56 N-m) using a torque wrench. Over-tightening damages the connector; under-tightening causes intermittent contact and poor return loss. Always use a torque wrench for measurement-grade connections.