Today, a wide variety of coaxial connectors can be used to meet the needs of today's high-frequency applications. Some common connectors have been discussed in this series, but other types exist that have not been mentioned. Although connectors may seem mundane, they are vital to any application. Therefore, it is important to understand the basics of coaxial connectors and the many options available today.
The N-type connector was introduced in 1942. This connector has a threaded connection and is still common today and is known for its durability. The standard N-type connector operates at 11 GHz, while some connector suppliers offer versions at 18 GHz. 50 Ω and 75 Ω versions are also available. N-type connectors comply with MIL-C-39012 specifications.
The SMA connector is widely used throughout the RF/microwave industry. It originated in the late 1950s and, similar to the Type N connector, the SMA connector (with 50 Ω impedance) uses threaded coupling. originally intended for use with semi-rigid coaxial cables with a diameter of 0.141 in, the SMA connector was later extended to flexible cables. the SMA connector uses a solid dielectric and, in addition, although the standard SMA connector operates in the frequency range DC to 18 GHz, some suppliers offer versions that can operate up to 26.5 GHz.
SMA connectors are mechanically compatible with two other connector types: 3.5 mm and 2.92 mm connectors. Both use an air dielectric and operate at higher frequencies than their SMA counterparts. 3.5 mm and 2.92 mm connectors are named after the inner diameter of their respective external conductors.
3.5 mm connectors first appeared in the 1970s and can achieve mode free performance up to 34 GHz, these connectors are known for their durability as they are designed to allow thousands of repeatable connections.
Even higher frequency performance can be achieved with 2.4, 1.85 and 1.0 mm connectors. Like the 3.5 mm and 2.92 mm connectors, the 2.4 mm, 1.85 mm and 1.0 mm connectors are also air-insulated. They also derive their name from the inner diameter of their respective external conductors.
Developed in the mid-1980s, 2.4 mm connectors can achieve performance up to 50 GHz. 2.4 mm connectors have a thick outer wall and are therefore not as fragile as SMA and 2.92 mm connectors. At first glance, it may be difficult to distinguish a 2.4 mm connector from a 2.92 mm connector. However, if one tries to connect a 2.4 mm connector to an SMA connector, the difference will be very clear - the two connector types will not match. Therefore, a suitable adapter is required to connect the 2.4 mm connector to an SMA, 3.5 mm or 2.92 mm connector.
In addition, 1.85 mm connectors can achieve mode free performance up to 65 GHz. Hewlett-Packard developed the connector in the mid-1980s. The company then made its design available as a public domain in 1988 to standardise connector types. 1.85 mm connectors can be mated to 2.4 mm connectors, but not to SMA, 3.5 mm and 2.92 mm connectors.
In addition, millimetre wave applications can utilise the 1.0mm connector. This connector has also been developed by HP and can achieve 110 GHz performance. The probe station is an example of an application utilising the 1.0 mm connector.
The widely used BNC connectors have a typical frequency range of dc to 4 GHz. the BNC connectors, which are typically used in test and measurement equipment, use bayonet coupling technology and have an impedance of 50 or 75 Ω. The female connectors have two bayonet lugs and can be connected to the male connectors by simply turning the coupling nut 1/4 turn. Unfortunately, BNC connectors cannot be used at frequencies above 4 GHz as they tend to radiate at these frequencies. BNC connectors are covered by MIL-C-39012.
TNC connectors are a threaded version of BNC connectors and have higher frequency performance than BNC connectors. These connectors are typically rated for 11 GHz. like the BNC connectors, the TNC connectors are also covered by MIL-C-39012.