RF COAXIAL CONNECTOR SELECTION
　It neds take into account of not only performance requests but also economic factors in connector selection. Performance must meet the needs of system wiring and economy must fulfil axiology. When selecting a RF coaxiall connector, The following four aspects need to be considered:
　Connector interface (SMA、SMB、BNC etc)
　Electric performance installation and cables
　Portconnect form (PC board cables panel etc;)
　Mechanical structure & plating (military、commericial)
1. Connector interface
　Connector interface is often determined by its application. At one time, it need meet electric and mechanical performance.
　With bayonet lock, BNC connector is often used in radio connection with frequency under 4GHz, network system, apparatus, instrument and Internet.
　TNC’s interface likes BNC’s except the screw interface It’s still used in 11GHz, and as good as in oscillation.
SMA connector is used widely in fields such as aviation, radar, microwave communication, digital communication and so on. Its impedance is 50Ω,frequency of flexible cable is under 12.4GHz, and maximum frequency of semrigid cable is 26.5GHz; type of 75Ω has widely applied foreground. The size of SMB is smaller than that of SMA. For its screw interface, it owns stronger mechanical performance and wider range of frequency. It is mainly used in military and can replace L9. frequency of commercial type 50Ω is up to 4GHz and 75Ω is 2GHz.
　Insulated material of type N screw interface connector id made from air. So it costs less. Its impedance is 450Ω or 75Ω, and frequency is up to 11GHz. This type is often used in area network、media spreading and apparatus testing.
　MCX series connector provided by Yongda company are at small size and connect reliable, which make it widely used in the telecommunication fields.

2. Electric performance、installation and cables
(1) Impedance
　Impedance of connector must match that of system and cable. It need notice that not all impedance of connector interface is 50Ω or 75Ω. If not match, it will make system performance decreased.
(2) voltage
　Make sure that working voltage is under maximum tolerance voltage.
(3) maximum working frequency
　All kind of connector have a maximum working frequency. Some 75Ω products for commercial use have a minimum working frequency limit.
　Every interface from has characterized except electric performance. For example: type BNC (bayonet lock) has facile installation and cheap price, widely used in low performance wiring; SMA、TNC series using screw coupling, meet the request for high oscillating environment; type SMB can join and cut rapidly, so become more and more popular.
(4) Transmit cable
　TV cable is often used in system only thinking over impedance for its small shield, a model application is TV antenna.
　TV flexible cable is a transmutation of TV cable. For its relative continuable impedance、better shield effect、flexible and low price, it is widely used in computer, but not in system requiring maximum shield.
　Shielded flexible cable dispel inductance and capacitance, mainly used in apparatus and building.
　Flexible coaxial cable become most popular airtight transmit cable for its special performance. Coaxial means signal and grounded conductor is coaxial. Its outside conductor is made of micromesh twist. So call it weaved coaxial cable too. This type of cable shield center conductor better. And its shield efficiency lies on basketwork material and thickens. It can suffer from high frequency, high pressure and extreme temperature.
　On semirigid coasial, out conductor is replaced with tubular crusts that improve shield effect in high frequency situation.
(5) installation
　There are two common methods to install connector: A、Weld center conductor and screw on shield layer. This method is designed for the situation of on special install tolls. B、Impact center conductor and impact into shield layer. The other methods derive from these, for example: weld center conductor and impact into shield layer. Because impact method makes high working efficiency and reliable weld performance, on the other hand, designing of special tools as-sure every connector is same, so this method will become more and more popular.

3. Portconnect form
　Connector provided by Yongda can be used in radio coaxial cable、 PCB and other connected interface. It has been proved by practice that special form connectors match special type cables. Small type coaxial connectors such as SMA、SMB link small diameter cable. Please consult cable size schedule in connector selection.

4. Mechanical structure & plating
　Structure affects connector price greatly. Design standard of connector includes military and commercial ones. Military standard according to MIL-C-39012, full copper material, Teflon insulation, inside and outside gold-plating, makes most reliable performance; commercial one uses cheap material, brass founder, polypropylene insulation, silver-piating.
　Materials used in connector are brass、beryllium copper and stainless steel. Center conductor use gold-plating for its small resistance、cauterantproof and good airtight. Military require SMA、SMB outside conductor plate gold and N、TNC、BNC plate silver. Because silver oxidized easily, lots of user likes gold-plating.
　Insulation often use 4 Teflon, polypropylene and tempered polypropylene. Among these 4 Teflon has best insulative performance, but price is high.
　Material and structure affect working difficulty and efficiency. So user need to select better performance-price radio according to application.