RF Connector Types Explained: SMA, N-Type, BNC, TNC, 1.0mm to 2.4mm Guide

SMA and the Subminiature Family

SMA is the default 50 ohm threaded interface for instrumentation, antennas and radios up to 26.5 GHz. It uses a 1/4-36 threaded coupling, a PTFE dielectric and a centre pin of roughly 0.9 mm. Its weaknesses are mechanical rather than electrical: the coupling nut is small, the recommended torque is around 0.8 to 1.1 N-m (7 to 10 in-lb), and a wrench used with too much enthusiasm will deform the hex and shift the reference plane. That single habit accounts for a large share of "this connector suddenly has high return loss" reports.

SMB is the snap-on version at the same scale, rated to about 4 GHz and used where quick mating matters more than bandwidth. SMP and SMPM are board-to-board blind-mate interfaces used in dense RF modules and phased arrays. SMP operates to roughly 40 GHz and SMPM to roughly 65 GHz, with a spring-loaded male side absorbing the axial tolerance that a blind mate cannot control. Where SMA is not enough but a full precision connector is hard to justify, 3.5 mm and 2.92 mm versions mate with SMA and extend the ceiling to about 33 GHz and 40 GHz.

SMA ConnectorSMA RF coaxial connector is a RF coaxial connector with a threaded connection mechanism developed and produced according to the US military standard MIL-C-39012. It ha...View Product →

N-Type, TNC and BNC: Larger Threaded and Bayonet Types

N-type connectors use a 5/8-24 thread and a much larger dielectric, which is why they handle far more power than SMA and stay stable outdoors. The standard ceiling is 11 GHz, with precision versions reaching 18 GHz. Properly mated and weatherproofed, an N-type pair is the normal choice for base station antenna feeders, jumper cables and outdoor radio units, and it tolerates the cable movement that would destroy a subminiature interface.

TNC is essentially a threaded BNC: the same body size, but screw coupling that holds under vibration, which is why it appears on mobile radio equipment and handheld test gear rated to about 11 GHz. BNC keeps its quarter-turn bayonet for fast patching and stops at about 4 GHz in 50 ohm form. The 75 ohm BNC used for video looks almost identical; mixing the two impedances into one RF path creates a mismatch that no amount of cable quality will fix.

N-type RF Coaxial ConnectorThe N-type series RF coaxial connector is a RF coaxial connector with a threaded connection mechanism developed and produced in accordance with the US military standar...View Product →

Precision Types for Millimetre-Wave Work

Above about 26.5 GHz the interface has to be air-dielectric and machined to tight tolerances. The 1.0 mm, 1.85 mm, 2.4 mm and 2.92 mm families share the same idea: no polymer around the centre conductor, tightly controlled bead geometry, and a reference plane defined at the mating face rather than somewhere inside the coupling nut.

Compatibility is where money quietly gets lost. SMA, 3.5 mm and 2.92 mm are intermateable. 2.4 mm and 1.85 mm mate with each other. 1.0 mm mates only with 1.0 mm. Forcing a worn, out-of-tolerance SMA onto a 2.92 mm or 2.4 mm test port can score that precision interface permanently, and a damaged test port quietly invalidates every measurement taken through it afterwards.

Hermetically Sealed and Other Specialist Types

Some RF paths are not allowed to leak. Hermetically sealed connectors replace the polymer bead with a glass-to-metal seal, so the dielectric is fused to the metal shell and the centre pin rather than pressed into it. Typical helium leak-rate specifications for such parts sit in the 10^-9 atm-cc/s range, and the mechanical strength comes from the seal itself rather than from an elastomer that will age.

These parts appear in vacuum chambers, pressure transmitters, cryogenic systems, aerospace payloads and any enclosure where condensation would change the dielectric constant and therefore the impedance of the line. The SMP and SMPM hermetic variants are common in dense microwave assemblies where a single sealed bulkhead has to pass several coaxial lines at once.

SMPM Hermetically Sealed ConnectorSMPM (SubMiniature Push-on Micro) sealed connector is a miniaturized RF connector with full escapement, semi-escapement, and light hole, designed for high frequency, c...View Product →

What Actually Decides the Choice on a Project

Frequency narrows the list to two or three candidates. Five practical constraints usually pick the final part.

• Cable compatibility. Connector series follow cable diameter, not preference. RG-316 and similar flexible cables suit SMA; RG-58 and RG-213 suit BNC, TNC and N-type; low-loss corrugated cable almost always terminates in N-type or 7/16.
• Impedance consistency along the whole chain. One 75 ohm part in a 50 ohm path produces a mismatch that shows up as return loss at exactly the frequency you care about.
• Mating cycles and torque. Standard SMA and N-type interfaces are generally quoted around 500 mating cycles; precision millimetre-wave interfaces wear faster and cost far more to replace.
• Environment. Outdoor units need an interface that seals when mated, plus the correct boot or tape wrapping. Vacuum and pressure boundaries need a glass-to-metal seal.
• Test-port protection. Keep a sacrificial adapter on bench instruments and inspect precision interfaces under magnification before every mate.

Attenuation, return loss and mechanical wear are linked more tightly than most specifications suggest; the practical causes of loss in a coaxial path are covered in this note on RF connector signal attenuation. For projects that need a specific interface, plating or cable termination, working with a manufacturer that machines its own parts usually shortens the loop between drawing and first article. Hanson Communication, an RF coaxial connector manufacturer based in Ningbo, produces SMA, N-type, TNC, BNC, precision and hermetically sealed interfaces as well as adapters and low-loss cable assemblies.