SMA connector is generally a connection between needle contact and hole contact. Whether the contact between two metal surfaces is good depends on the material (different metal conductivity), contact pressure, and actual contact surface junction. Therefore, there are five aspects to consider when choosing an SMA connector.
1. Type of interface mechanism
The connection mechanism of the connector is not only to provide convenient and rapid connection or separation of coaxial transmission lines, the key is to provide stable electrical performance and environmental protection device, when there is not enough space to rotate the connection nut, should choose the non-torsion type connection mechanism. For frame connectors, non-torsional connection mechanisms are also useful.
2. Electrical performance
A. Characteristic impedance: The connector must match the impedance of the transmission system and cable; otherwise, the system performance will be degraded;
B. Voltage resistance: the maximum voltage resistance value of the connector should meet the voltage resistance requirements for system use;
In GENERAL, in wide-band applications, some of the favorable wideband impedance matching characteristics are sacrificed to obtain the desired high voltage rating.
C. Maximum working efficiency.
3. Cable installation method and cable type
A. Cable connection: There are two ways to install the connector cable: one is to weld the center conductor, and the standard tightness method of combing and weaving the wire is still common, especially applicable to the occasions without special installation tools and easy to maintain on site. two Welding center conductor, clamping method of pressing braided layer. Due to the high efficiency of crimping method. The performance of terminal is reliable and consistent, which has become a common method nowadays.
B. Cable type: Select appropriate connectors according to the characteristics of various types of cables (such as flexible cables, semi-rigid cables, corrugated conductor insulated cables, and foam insulated cables). Generally, cables with small outer diameters are suitable for small connectors.
4. Terminal form
Connectors can be used for RF coaxial cables, printed circuit boards, frame drawer-type functional components and their connecting interfaces.
5. Material and coating
Shell and inner conductor are mainly brass, beryllium copper, tin bronze, insulation material is mainly tetrafluoroethylene.
The center conductor is generally plated with silver or gold, and the shell is plated with nickel or silver. SMA, SMB, SSMB, SMC outer conductors are all gold plated.
Rf coaxial connectors are used to transmit rf energy in the frequency range of 18GHz or higher. The basic structure includes:
Positive and negative neutral contact parts, the outer interface material, the outermost contact parts, the outer part plays the same function as the cable outer shielding layer: signal transmission, shielding and grounding.
Material coating, interface, performance, installation method according to the needs of different instruments, to choose different specifications of SMA connectors. Let's simply take the material coating, the pin or terminal of the connector, there will be a layer of coating, such as lead-tin alloy, pure tin, nickel plating, silver plating, silver-palladium alloy, gold plating, and so on. When the components are connected, the conductivity of different coated metals is different, and the corresponding contact resistance is also different. For example, the conduction of gold is certainly the best, but because of the high price of gold, so according to the cost of connector production to consider the coating. We need to consider these issues when choosing SMA connectors.
