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 (e.g., SMA, SMB, BNC, etc.)
• Electrical performance and cable compatibility
• Termination type (e.g., PCB, cable, panel)
• Mechanical design 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 specifications. Different types are suited for different environments and frequency ranges.
The BMA connector is commonly used in low-power microwave systems up to 18 GHz, particularly for blind-mate applications. It offers a reliable connection in compact designs.
BNC connectors are bayonet-style and ideal for RF connections below 4 GHz. They are widely used in networking, test equipment, and computer systems due to their ease of use and affordability.
TNC connectors share the same interface as BNC but feature a threaded coupling, allowing them to perform reliably at higher frequencies—up to 11 GHz—especially in vibration-prone environments.
SMA connectors are popular in military and civilian applications such as radar, satellite communication, and digital systems. They operate at 50Ω and can handle frequencies up to 12.4 GHz with flexible cables, and even higher with semi-rigid cables. 75Ω versions are gaining traction in digital communications.
SMB connectors are smaller than SMA and use a self-locking mechanism for quick mating, making them ideal for high-speed data applications. For example, L9 connectors offer 50N up to 4 GHz and 75Ω up to 2 GHz.
SMC connectors are similar to SMB but use a screw coupling, offering better mechanical strength and a broader 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 suitable for frequencies up to 11 GHz and are commonly found in regional networks, testing equipment, and media transmission systems.
RFCN’s MCX and MMCX series are compact, reliable, and ideal for miniaturized and high-density designs, offering excellent performance in modern electronics.
2. Electrical Performance, Cable, and AttachmentA. Impedance:
Impedance matching between the connector and the system is crucial. Not all connectors are 50Ω or 75Ω, so mismatched impedance can lead to signal loss and reduced system performance.
B. Voltage Rating:
It's important to ensure that the connector's maximum voltage rating is not exceeded during operation, as this could cause damage or failure.
C. Maximum Operating Frequency:
Each connector has a specific frequency range. Some commercial or 75Ω designs may have a minimum operating frequency. For instance, BNC connectors are known for their ease of installation and lower cost, making them suitable for low-frequency applications. SMA and TNC connectors, on the other hand, are preferred in high-vibration environments due to their secure screw coupling. SMB connectors provide a fast connect/disconnect feature, which is increasingly popular among users.
D. Cable Selection:
Television cables are often used in systems where impedance is the main concern, though their shielding is limited. They are commonly used for TV antennas.
TV flexible cables are a variation of television cables, offering better impedance continuity and improved shielding. They are bendable, affordable, and widely used in the computer industry, but not ideal for high-shielding applications.
Shielded flexible cables eliminate the need for additional components like inductors and capacitors in instrumentation and building systems.
Flexible coaxial cables are the most common type of closed transmission cable due to their unique structure. They consist of a central conductor surrounded by a braided outer shield, providing good electromagnetic interference (EMI) protection. Their shielding effectiveness depends on the braid density and material.
Semi-rigid coaxial cables replace the braided shield with a solid metal tube, offering superior shielding at high frequencies. These are typically used in high-frequency applications.
E. Cable Attachment Methods:
There are two primary methods for attaching cables to connectors: soldering the center conductor and screwing the shield, or crimping both the center conductor and shield. Other methods include welding the center conductor and crimping the shield.
The soldering method is often used when no specialized tools are available. However, crimping is more efficient and provides a reliable connection. With the development of low-cost crimping tools, this method is becoming more popular, especially for high-volume production.
3. Termination TypeRF coaxial connectors are designed for various termination types, including PCB mounting, cable ends, and panel mounting. It's important to match the connector size with the cable diameter. For example, small-diameter cables are typically paired with SMA, SMB, or SMC connectors.
Referencing a cable size chart can help in choosing the appropriate connector for each application.
4. Mechanical Construction and PlatingThe mechanical design of a connector significantly impacts its cost. Military-grade connectors follow strict standards, using materials like copper, PTFE insulation, and gold plating for optimal performance. Commercial-grade connectors, on the other hand, use more cost-effective materials like brass, polypropylene, and silver plating.
Common materials for connectors include brass, beryllium copper, and stainless steel. The center conductor is usually plated with gold for low resistance, corrosion resistance, and good sealing. Military-grade connectors often require gold plating for SMA and SMB, while N, TNC, and BNC connectors may use silver plating. However, many users prefer nickel plating due to silver’s tendency to oxidize.
Insulators in connectors are typically made from PTFE, polypropylene, or polystyrene. Among these, PTFE offers the best insulation performance but comes at a higher cost.
The material and construction of a connector affect its manufacturing complexity and efficiency. Therefore, it's important to choose a connector that balances performance, durability, and cost based on the intended application environment.
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