SMA vs RP-SMA: How to Tell Them Apart (and Why It Matters)

Published on 10/13/2026

An antenna screws onto a router, but the link barely works. The shell fits; the center contacts do not. SMA and RP-SMA use similar threaded bodies, so thread engagement alone is not proof of a valid RF connection.

SMA and RP-SMA differ in the center contact, not in signal polarity. A standard SMA plug has internal threads and a pin. An RP-SMA plug has internal threads and a socket. The corresponding jacks have external threads, with a socket for SMA and a pin for RP-SMA.

This guide focuses on inspection and ordering, rather than another general connector catalogue. Check the coupling body and the center contact separately. That two-part description is far safer than a supplier listing that says only "male SMA".

SMA vs RP-SMA identification table

Identify the connector from the mating face. Internal threads sit inside a coupling nut; external threads sit on the jack body. A pin projects into the mating connector. A socket receives that pin. Do not identify a connector from the cable exit, the bulkhead nut or a photograph of the rear.

The conventional SMA coupling thread is 1/4-36, approximately 6.35 mm nominal diameter with 36 threads per inch. RP-SMA uses the same coupling arrangement. A thread gauge or ruler can help distinguish families, but it cannot distinguish standard from reverse polarity. You must inspect the center contact.

Which connector pairs actually mate?

Mate standard SMA to standard SMA, or RP-SMA to RP-SMA, using complementary plug and jack bodies. A cross-polarity pair can have compatible shells while presenting two sockets or two pins. Two sockets leave the signal path open. Two pins can collide and damage a connector or equipment port.

If a standard SMA antenna must connect to an RP-SMA device, use an adapter whose two ends are specified independently. "SMA to RP-SMA" is not a complete specification. It does not tell you whether either end has internal or external threads, or a pin or socket.

Frequency, loss and application choices

Reverse polarity does not reverse voltage, invert phase or turn a 50 ohm cable into a different impedance. Both interfaces are used in 50 ohm RF systems. Frequency rating, VSWR, insertion loss and power handling belong to the selected connector and assembly datasheets, not to the letters RP alone.

RP-SMA is common on Wi-Fi antenna connections, including 2.4 GHz equipment. Standard SMA is common on cellular, GNSS and test equipment. These are useful expectations, not identification rules. At 5 GHz or 6 GHz, verify the actual product rating and assembly insertion loss across the full band. An antenna labelled "Wi-Fi" does not settle its connector polarity.

Avoid adding an adapter merely to use a spare cable. Each extra interface introduces another contact to inspect and another potential mismatch. A correctly terminated cable usually makes a cleaner permanent installation. For routing and strain relief, read SigmaRF's RF Cable Assembly Design Guide: PCB to Antenna Reliability. For board-side connections, the RP-SMA to MHF4 Antenna Pigtail article addresses a different problem: the miniature module interface.

Worked ordering example

Suppose a router port has external threads and a visible pin. Inspection identifies an RP-SMA jack. A remote antenna also has an RP-SMA jack. The extension cable therefore needs an RP-SMA plug on both ends: internal threads and a socket at each end. Two "female" equipment ports can require a "male-to-male" cable even though both equipment ports contain pins.

If the antenna instead has a standard SMA jack with a socket, change End B to a standard SMA plug with a pin. Do not change End A. Mixed-polarity cable assemblies are valid when each end matches its own equipment port. That is different from directly mating incompatible connector faces.

Mistakes that damage ports

SMA and RP-SMA FAQs

Bottom Line

The dependable identification rule is simple: inspect threads and contact. Never buy from a gender label alone when replacing an antenna pigtail. Include both mating-face descriptions in the RFQ and check them again before connecting equipment.

SigmaRF supplies custom coaxial cable assemblies through its Vadodara volume facility and Cleveland-area precision facility. Every assembly is VNA-swept for VSWR and insertion loss before shipment. Its testing capability spans 100 MHz to 40 GHz; that does not mean every SMA or RP-SMA assembly is rated to 40 GHz. Lead times can be as short as 2 days, subject to the build and component availability.