What are RF connectors?
RF connectors are connectors used to make electrical connection for signal transmission in radio frequency applications. These connectors are used in wide variety of applications range from 0 to 18 GHz and above.
All types of RF connector have one male connector and one female connector. Male connectors are often called plug and female connectors as jack. Center pin and outer grounding with locking mechanism provides it a strong and reliable connection.
Selection of an RF connector depends on the specifications like frequency range, performance, size and shape of each connector types. Here are the most commonly used RF connectors:
BNC
BNC is one of the 
commonly used connectors at low frequency RF applications. It is an easy to use connector with rigid body and locking mechanism. BNC connector has the simplest design among other connectors.
Operating frequency: 0 to 4GHz
Applications: video signals, amateur radio, timing / clock signals and instrumentation.
SMA
SMA connector is one of the most suitable RF connectors at UHF and most part of the SHF range. Smaller size and reliable performance makes SMA connector favorite choice for RF engineers.
SMA connectors are one the best performing connectors in terms of impedance matching. Most common type is 3.5 mm connector.
Operating frequency: 0 to 18 GHz
Applications: GSM, CDMA, radio communication boards, RF power amplifiers, RF isolator, power splitters, directional couplers, Wi-Fi antennas and low power UHF communication systems.
SMB
SMB is another rigid, easy to use RF connector with lower cost and customized shape for variety of application. It’s simple design suitable for an easy connection and disconnecting without any difficult mechanism of locking threads. SMB connector offers better performance at below 4 GHz frequency.
Operating frequency: 0 to 10 GHz
Applications: Medical equipments, base stations, low power UHF communication systems and radio applications.
N-type
N-type is medium sized RF connectors suitable for durable applications. It offers a stable performance up to 11 GHz. N-type has a thread locking mechanism which provides strong and reliable connection.
There are water proof n-type connectors available for specific applications. Most of the RF test equipment uses N-type as its default connector solution due to its durability and performance. It is a good choice for well matched impedance applications.
Operating frequency: 0 to 12 GHz
Applications: RF equipments, base stations and low power and high power UHF communication systems, satellite systems and RADAR systems.
Other low frequency connectors
PL-259
PL-259 is one of the oldest RF connector used for low frequency applications such as amateur radio and marine communication systems. It has a strong structure, easy to assemble with coaxial cable and still popular among radio enthusiasts.
Operating frequency: Below 200 MHz
Applications: Mainly in amateur radio applications, shortwave radio, timing signal systems, and low power HF communication systems.
SO-239
SO-239 is yet another low frequency RF connector typically used in applications below 100 MHz range.
Operating frequency: Below 100 MHz
Applications: amateur radio and shortwave radio applications.
Conclusion
RF connectors are available in many size shape and frequency range to fit wide variety of applications. It has to be selected according to the specification required for particular applications. RF connector adaptors are used to connect between two different standards.
PL259 and SO239 connectors are also called “UHF” connectors even though they don’t work very well at UHF frequencies (The term comes from the early days of Radar when everything above 30MHz was regarded as “Ultra High”)
Other types of RF connector:
F -type: Used in Cable/Satellite and (in some countries) Terrestrial TV reception
Belling Lee: Used for TV aerials in Britain and elsewhere they were originally designed for MW/AM radio and therefore are not as good as F-type
Phono: Yes the RCA phono connector originally developed for audio. Sometimes seen on TV tuners and UHF modulators.
Hello Mike, thanks for highlighting.
You are right, PL259 and SO239 connectors are used by low frequency analogue radio / TV application.
I will add them to the list.