When selecting RF coaxial connectors, it's essential to balance both performance and cost. The chosen connector must meet the electrical requirements of the system while also aligning with value engineering principles. In general, four key factors should be considered when making a selection.
• Connector interface type (e.g., SMA, SMB, BNC, etc.)
• Electrical performance and cable compatibility
• Termination type (e.g., PCB, cable, panel)
• Mechanical construction and plating (military or commercial grade)
The choice of connector interface is typically driven by the application, but it must also satisfy both electrical and mechanical performance needs.
SMA connectors are widely used in military and civilian applications such as aviation, radar, and microwave communication. They operate at 50Ω with flexible cables up to 12.4GHz, and up to 26.5GHz with semi-rigid cables. Some models also support 75Ω for digital communications.
BNC connectors are bayonet-style and suitable for RF connections below 4GHz. They are commonly found in networking, instrumentation, and computer systems due to their ease of use and affordability.
TNC connectors are similar to BNC but feature a threaded connection, making them more reliable under vibration. They can operate up to 11GHz and are often used in high-performance environments.
SMB connectors are smaller than SMA and use a self-locking mechanism for quick mating. They are ideal for digital communication systems, with typical operating frequencies up to 4GHz for 50Ω and 2GHz for 75Ω.
SMC connectors are similar to SMB but use a threaded design, offering better mechanical strength and a wider frequency range. They are often used in military or high-vibration settings.
N-type connectors use air as an insulator, making them cost-effective. Available in 50Ω and 75Ω, they are commonly used in regional networks, media transmission, and test equipment up to 11GHz.
MCX and MMCX series connectors from RFCN are compact and highly reliable, making them ideal for miniaturized and high-density applications. Their small size and excellent contact performance make them popular in modern designs.
2. Electrical Performance, Cable, and AttachmentA. Impedance: Connectors must match the system and cable impedance. Not all connectors are 50Ω or 75Ω, so mismatching can lead to signal loss or degradation.
B. Voltage Rating: It’s important to ensure that the connector can withstand the maximum voltage of the system during operation.
C. Frequency Range: Each connector has a specific frequency range. For example, BNC is best suited for low-frequency applications, while SMA and TNC are preferred for high-vibration environments. SMB connectors offer fast mating and are gaining popularity in high-speed systems.
D. Cable Types: Television cables are used where impedance matching is the main concern, though they have poor shielding. TV flexible cables offer better shielding and flexibility, making them suitable for computers, but not for high-shielding applications.
Shielded flexible cables reduce the need for additional components like inductors and capacitors. Coaxial cables, with their central conductor and braided outer shield, provide good electromagnetic interference (EMI) protection. Semi-rigid cables replace the braid with a solid tube, improving high-frequency performance.
E. Cable Attachment: There are two primary methods: soldering and crimping. Soldering is common when no specialized tools are available, while crimping offers higher efficiency and reliability. As crimping tools become more affordable, this method is becoming increasingly popular.
3. Termination TypeRF coaxial connectors are available in various termination types, including PCB, cable, and panel mounting. Smaller cables typically connect to smaller connectors like SMA, SMB, and SMC. Always refer to a cable size chart to choose the right connector for your application.
4. Mechanical Construction and PlatingThe mechanical design of a connector significantly affects its cost. Military-grade connectors follow strict standards, using materials like copper, PTFE insulation, and gold plating for maximum reliability. Commercial-grade connectors may use brass, polypropylene, and silver plating to reduce costs.
Connectors are made from materials like brass, beryllium copper, and stainless steel. Gold plating is common for the center conductor due to its low resistance and corrosion resistance. Military standards often require gold plating on SMA and SMB, while N, TNC, and BNC may use silver. However, many users prefer nickel plating due to silver's oxidation issues.
Common insulating materials include PTFE, polypropylene, and polystyrene. PTFE offers the best insulation but is more expensive. The material and design of the connector affect manufacturing complexity and cost, so choosing the right connector based on application needs is crucial.
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