Coaxial connectors are grouped into categories based on their physical size and cable compatibility: standard, miniature, subminiature and micro-miniature. The standard size category includes the earlier designs: N, C, SC, HN, and 7/16. The miniature category is composed mainly of BNC and TNC. The sub-miniature category holds most of the currently used connectors in use above 1 GHz: SMA, SMB, SMC, SMP, GPO®, APC (7 mm), K™ (2.9 mm), and BMA (Blind-mate). The micro-miniature category is generally for small size and includes MCX, MMCX, SSMA, SSMB, SSMC, SSMP®, and GPPO®. The following information is general in scope about the most commonly used connectors; connector specifications may vary by manufacturer, and SSI or the connector manufacturer should be contacted for more details. Representative values for certain connectors are listed in Table 4 and 5, but be aware that the values given are an average of manufacturers and actual values may be different.
50-Ohm connectors are available in all the common connector types; other impedances are available in most types. A variety of configurations and mounting styles are available; straight, right angle, bulkhead, flange, surface mount, and others, in both plug and jack, soldered or crimp versions. An easy definition of a plug is having a movable mechanism for a connector coupling, while jacks utilize the stationary feature of a coupling design. Generally, flexible cables utilize a crimped connector attachment, while connectors are soldered or welded semi-rigid cables. Common metals used to fabricate connector’s conductors can be plated to minimize signal losses and increase the durability, normally with gold, nickel, or silver. Plating may become more important at higher frequencies due to skin effect and the possible effects of oxidation or corrosion.
TABLE 4 – CONNECTOR FREQUENCY RANGE
N type connectors are generally used with coaxial cables ranging from .350 to .400 OD, with a threaded coupling. They exhibit low VSWR across a frequency range of 0 to 11GHz (also available in precision types up to 18GHz). The N connector is the most popular standard size connector, with good vibration and environmental characteristics. Applications include test equipment, LANs, broadcast, satellite, and military communication equipment.
BNC connectors have a frequency range of 0 to 4 GHz, and are used primarily with cable sizes of .150 to .250” OD. Coupling is a quick connect/disconnect bayonet particularly useful in test equipment. BNC applications include communication, medical equipment, instrumentation, and computer peripheral interconnections. TNC connectors are BNC connectors with threaded couplings and improved performance at higher frequencies (0 to 11 GHz, precision types to 18GHz), with low noise and better shock and vibration characteristics. TNC connectors are commonly used in military and aerospace applications where performance is required under vibration.
SMA connectors are semi-precision 3 mm high frequency connectors, originally used with .141” semi-rigid cable, but now produced for use with both flexible and semi-rigid cable from .047 to .250” OD with threaded coupling interfaces. SMA connectors give repeatable electrical performance from 0 to 18 GHz (up to 26.5 GHz with improved versions), and are widely used in microwave systems where size reduction, minimum attenuation, and low VSWR are required.
SSMA connectors are smaller versions of the SMA for use with cable diameters down to .047 OD. The SSMA has a frequency range up to 40 GHz.
The 2.4 mm connector has been developed to offer higher frequency operation up to 50 GHz. The 2.4 mm size is smaller than an SMA, but the interface is more rugged and therefore more reliable, although probably at a higher price.
2.9 mm connectors are compatible with SMA connectors and have a frequency range up to 46 GHz.
SMB connectors have a quick connect/disconnect interface mechanism, which offers good performance (up to 4 GHz) with low reflection under moderate vibration. Typical applications are in telecommunications, instrumentation, wireless, PC/LAN controls, and inter-or intra-board connections of RF or digital signals.
SMC connectors are similar to SMB, but with a threaded coupling interface. Tighter control of the contact and insulator locations allow the SMC to operate up to 10 GHz. SMC connectors are used primarily in microwave telephony and other non-military telecommunication requirements.
The MCX connector is similar to the SMB (up to 6 GHz), with quick connect/disconnect, but smaller in size and lighter in weight. Applications include telecommunications, instrumentation, wireless, controls, and PC/LAN.
BMA connectors have snap-on couplings, especially designed for blind-mate applications in low power systems up to 18GHz.
SSMB connectors are smaller versions of the SMB and for use with cable diameters down to .047 OD. The SSMB has a frequency range up to 12.4 GHz.
The GPO® connector is a push-on, blind-mate connector that has a greater frequency range than the BMA (extended range up to 40 GHz), and can tolerate up to 0.010” radial and axial misalignment with negligible VSWR change.
The SSMP® (GPPO®) connector is a smaller, lighter weight version of the SMP (GPO™) with a frequency capability up to 65 GHz.