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​SMA Connectors: Definitions & Common Types at a Glance​

June 13,2025

1. What is an SMA connector?

Fundamental Definitions

The semi-precision RF coaxial connector SMA is acronym “Subminiature version A”. Designed by Bendix Corporation in 1960 as a micro-connector interface for coaxial cables with helical coupling mechanisms, the “A” reflects its miniaturized form.

图片 11
SMA connector image from tejiate

Features of Performance

  • ImpedanceStandard: Usually establishing 50 Ω impedance connections with external antennas (GPS, Bluetooth, cellphone, Nordic, and XBee), impedance of 50 Ω Standard for most RF applications and highly common impedance in RF systems, this guarantees low signal loss and maximum efficiency transmission.
  • Frequency Range: Standard MIL-STD-348defined in the United States While high-frequency connectors handle5 GHz+ general connectors cover DC-18 GHz.
  • Voltage Standing Wave Ratio (VSWR): Acronym for “Voltage Standing Wave Ratio,” a crucial measurement in RF systems gauging impedance matching quality. Higher VSWR values suggest reduced signal transmission efficiency and potential for multiple signal reflections. This lowers system efficiency, significantly compromises signal quality, and runs the danger of equipment and gearbox line damage.
Design Strategy VSWR Insertion Loss Application Scenery
Simple Monopole Antenna ≤2.0 Low (<0.5 dB) Consumer Electronics (Priority of Cost)
Broadband Matched Antenna ≤1.3 Medium (∼1.2 dB) Base Stations (Performance Focus)
Metamaterial Antenna ≤1.1 High (>2 dB) High-Precision Radar (Matchable Efficiency Sacrificed)

  • Core Formula: VSWR = (1 + Γ) / (1 – Γ)​

    Numerical Ranges:

    Precision Systems: VSWR ≤ 1.2​

    Consumer Electronics: VSWR ≤ 2.0​

    High-Frequency Broadband: VSWR ≤ 1.07 + 0.04√f (GHz)​

    Mating Durability: Per IEC 60512-23-3, the standard specification for SMA connectors provides minimum 500 mating cycles; military-grade variants provide extended lifetime.

2.What are the SMA Connector Types?

Classified by Polarity

  • Standard Male (SMA-J) :Internal 1/4-36 (Outer Diameter: 1/4 inch, 36 threads/inch) + 5/16 inch hex nut, with male pin.
  • Standard Female (SMA-K):External 1/4-36 (Outer Diameter: 1/4 inch, 36 threads/inch), with female socket.
  • Reverse Polarity Male (RP-SMA-J):Internal 1/4-36 (Outer Diameter: 1/4 inch, 36 threads/inch) + 5/16 inch hex nut, without male pin but with female socket.
  • Reverse Polarity Female (RP-SMA-K):External 1/4-36 (Outer Diameter: 1/4 inch, 36 threads/inch), without female socket but with male pin.
  •  
Structure Diagram of RF Connector

Structure Diagram of RF Connector

Structure Diagram of RF Connector

 

Connector TypeCenter Contact StructureOuter Conductor Structure
Standard Male (SMA-J)
Internal Threads + Male Pin
External Threads + Inner Bore
Standard Female (SMA-K)
External Threads + Female Socket
Internal Threads + Outer Pin Sleeve
Reverse Polarity Male (RP-SMA-J)
Internal Threads + Female Socket
External Threads + Outer Pin Sleeve
Reverse Polarity Female (RP-SMA-K)
External Threads + Male Pin
Internal Threads + Inner Bore
  • Reverse Thread (RT-SMA): Features threads with the opposite direction to standard SMA connectors. This is another variant of SMA connectors, designed to prevent cross-connection between devices of incompatible connector types.

Classified by Physical Form

  • Straight：No bending, signal path typically linear.
  • 45°Angle：Balanced solution optimizing space and signal performance, common in specific scenarios like radar modules.
  • Right Angle：Designed with 90°bend for compact and tidy connections.
  • Swivel Right-Angle：Rotatable head (360°) prevents cable twisting.

Classified by Mounting Method

  • Flange Mount/ Panel Mount: Most prevalent installation type, ideal for PCB connections requiring high-strength fixation.
  • Through-Hole – TH: Pins inserted into plated through-holes + soldered on the backside, suited for medium-to-low density PCB connections with basic requirements.
  • SMT (Surface Mount Type): Designed for direct soldering to PCB surface pads, eliminating nut fixation required for panel-mount SMAs.

Classified by Mounting & Termination Methods

  • Crimp: Uses tools to crimp cables – rapid, reliable, suitable for mass production and high-volume cable assembly.
  • Solder: Directly soldered to cables or PCBs – low cost but inefficient, ideal for low-volume or customized cables.
  • Snap On: Tool-free quick installation with repeatable plugging/unplugging – moderately priced.
  • Press Fit: Pressed into PCB plated through-holes via machine/press – higher cost.
  • Quick Disconnect: Designed for high-frequency plugging/unplugging, emergency disconnection, or accidental-touch prevention. Features a mechanical locking/unlocking mechanism enabling second-level connection/disconnection while maintaining stable RF performance – very high cost.

Classified by Application Scenarios

  • General Purpose:Frequency range: DC-18 GHz, Material: Brass.
  • Hermetic Sealed：Corrosion-resistant, supports extreme environments (vacuum/pressurized). Material: Stainless steel.
  • HF/Microwave (SMA 2.9 Series):Frequency range: DC-27 GHz, Compatible with 2.92mm/Type-K interfaces.
  • Multi-Port (Common 18/25/32 ports):Integrated multi-port configurations (8/12/24 ports) for complex RF systems.
​SMA Connector Selection Flowchart

3. What is SMA Used For?

Based on the design characteristics of SMA connectors, they are most commonly used for handheld radios and mobile phone antennas, and in the 21st century, primarily employed for Wi-Fi antennas. Currently, devices requiring coaxial connections widely apply them, providing signal interconnections for RF components. While also delivering RF connections between circuit boards, many microwave components (including filters, attenuators, mixers, and oscillators) utilize SMA connectors.

Core Irreplaceable Advantages of SMA Connectors

Characteristic Legacy Connector (e.g., BNC) SMA Connector
Max. Frequency ≤4 GHz 40 GHz
Power Handling ≤100 W 500 W (RMS)
Mechanical Stability Threads prone to loosening Torque Locking (>80 N·cm)
Miniaturization Outer Diameter ≥10 mm Outer Diameter ≤6 mm

Find the Right SMA Connectors, Cable Assemblies & Adapters

Tejiate offers a diverse range of SMA connectors and adapters. Whether you’re using RG-178 micro cables (Φ1.8mm), LMR-400 thick cables (Φ10.3mm), or require fully customized solutions – we meet your exact requirements.

  • Our team will answer your inquiries within 12 hours.
  • Your information will be kept strictly confidential.

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