When sourcing components for an RF system, SMA connectors (SubMiniature version A) are arguably the most common interfaces you will purchase. Designed for use from DC up to 18 GHz (and up to 26.5 GHz for “Super SMA” variants), they are ubiquitous in telecommunications, Wi-Fi routers, and laboratory testing.
However, procuring them is notorious for one major pitfall: confusing Standard SMA with Reverse Polarity SMA (RP-SMA). Ordering the wrong polarity or gender will bring your assembly line or testing schedule to a grinding halt. If you are looking for a broader overview of all RF interfaces, you can refer to our general guide on coaxial connectors. But if you need to buy SMA connectors today, this guide will ensure you get it right.
We provide specialized solutions up to 40 GHz.
Quick Visual Identification Table
The confusion stems from the fact that “Male/Female” refers to the threads on the outside, while the center pin determines the polarity. Here is the ultimate cheat sheet:
| Connector Type | Thread Type (Outside/Inside) | Center Contact (Pin/Receptacle) | Common Application |
| Standard SMA Male | Threads on the INSIDE | Has a center PIN | RF Cables, Test Equipment |
| Standard SMA Female | Threads on the OUTSIDE | Has a center RECEPTACLE (hole) | Device Chassis, Amplifiers |
| RP-SMA Male | Threads on the INSIDE | Has a center RECEPTACLE (hole) | Wi-Fi Antennas |
| RP-SMA Female | Threads on the OUTSIDE | Has a center PIN | Wi-Fi Routers, Drones |
1. The Standard SMA
Standard SMA connectors follow the traditional rule of RF hardware: the male connector has the pin, and the female connector has the receptacle.
- Buyer’s Tip: Standard SMA is the default for almost all professional RF and microwave equipment, including cellular base stations, SDRs (Software Defined Radios), and laboratory measuring instruments. If your engineers ask for an “SMA Cable,” they almost certainly mean Standard SMA.
2. The RP-SMA (Reverse Polarity) Trap
Reverse Polarity SMA was intentionally created by the FCC in the late 1990s to prevent consumers from attaching high-gain, professional Standard SMA antennas to consumer Wi-Fi equipment. It “reverses” the center pin geometry.
- Buyer’s Tip: If you are buying components for consumer-grade Wi-Fi routers, Bluetooth devices, or consumer drone video transmitters, you will likely need RP-SMA. Never try to force an RP-SMA male into a Standard SMA female—you will smash the center receptacles together and permanently destroy both connectors.
3. Key Specifications to Check Before Buying
Beyond gender and polarity, ensure these specs match your BOM (Bill of Materials):
- Material: Brass with gold plating is cost-effective and great for static installations. For lab environments where cables are constantly connected and disconnected, pay the premium for Passivated Stainless Steel to prevent thread wear.
- Impedance Mismatch: A poorly machined SMA connector will introduce unwanted reflections into your transmission line, negatively impacting your system’s VSWR and Return Loss. Always request the VSWR specs from your supplier (a good SMA should have a VSWR of < 1.15:1 at 18 GHz).
- Frequency Rating: Don’t assume all SMAs go to 18 GHz. Cheap, commercial-grade SMAs may fail above 6 GHz. If you are operating in the Ku-band or K-band, you must specify “Precision SMA” or “Super SMA.”
Procurement Checklist:
- [ ] Did I verify the center pin/receptacle against the thread type?
- [ ] Is this for professional RF (Standard SMA) or consumer Wi-Fi (RP-SMA)?
- [ ] Did I choose stainless steel for high-mating-cycle laboratory use?
Conclusion
Buying SMA connectors shouldn’t be a guessing game. By strictly defining the gender and the polarity (Standard vs. RP), and matching the material to the use-case, procurement teams can eliminate costly RMA returns and keep engineering projects on track.
Frequently Asked Questions (FAQ)
Q1: Can I connect an SMA to an RP-SMA?
No, they are mechanically incompatible. An RP-SMA male and a Standard SMA female both have center receptacles (holes). If you try to connect them, there will be no electrical connection. You must use a dedicated SMA to RP-SMA adapter.
Q2: How many times can I connect and disconnect an SMA connector?
This is known as the “mating cycle.” Standard brass SMA connectors are typically rated for around 500 mating cycles. Passivated stainless steel connectors can last for thousands of cycles, making them necessary for test labs.
Q3: Do SMA connectors need to be torqued?
Yes. For optimal electrical performance and to prevent damaging the center pin, SMA connectors should be tightened using a calibrated 5/16-inch torque wrench, typically set to 8 in-lbs (0.9 N-m).