Do you often wonder whether to choose an SMA connector or a 2.92mm connector? You may also murmur, can the 3.5mm connector and the SMA connector be directly connected? Today we will specifically talk about this topic. First, let’s get to know these types of connectors

SMA connector

The SMA-type RF coaxial connector was designed by Bendix and Omni-Spectra as an OSM connector in the late 1950s. It was one of the most commonly used RF/microwave connectors at that time. Initially, SMA connectors were designed for 0.141″ semi-rigid coaxial cables and precision connectors for microwave applications in the military industry. They were filled with PTFE dielectric. Under the conditions at the time, due to the small size of SMA connectors, It can work at higher frequencies (the frequency range for mating semi-rigid cables is DC~18GHz; when mating flexible cables, it is DC~12.4GHz), and it is quickly popularized. Even millimeter-wave connectors developed later (such as 3.5mm, 2.92mm) also consider the issue of mechanical compatibility.

SMA connector

3.5mm connector

The 3.5mm connector is a connector with an inner diameter of the outer conductor of 3.5mm, a characteristic impedance of 50Ω, and a connection mechanism of 1/4-36UNS-2 inch threads. In the mid-1970s, Hewlett-Packard and Amphenol of the United States (mainly developed by HP, and the early production was carried out by Amphenol) introduced a 3.5mm connector with a working frequency of up to 33GHz. This is the earliest available radio frequency coaxial connector in the millimeter-wave band. One obvious difference with SMA connectors (including Southwest Microwave’s “Super SMA”) is that 3.5mm uses an air medium.

The outer conductor of the 3.5mm connector is thicker than the SMA connector, and its mechanical strength is better than that of the SMA connector. Therefore, not only the electrical performance is better than the SMA connector, but also the mechanical durability and performance repeatability is higher than that of the SMA connector, so it is more suitable for use in the testing industry.

SMA connector

2.92mm connector

2.92mm connector (some manufacturers call this connector a 2.9mm or K-type connector and some manufacturers call it SMK, KMC, WMP4 connector, etc.). The inner diameter of the outer conductor is 2.92mm, the characteristic impedance is 50Ω, and the connection The mechanism is a radio frequency coaxial connector with 1/4-36UNS-2 inch threads. Its structure is similar to the 3.5mm connector but smaller.

In 1983, Wiltron’s William.Old.Field senior engineer developed a new type of 2.92mm/K type connector on the basis of summing up and overcoming the millimeter-wave connector introduced before (K type connector is a trademark of Wiltron) ), the diameter of the inner conductor is 1.27mm, which can be plugged with SMA and 3.5 connectors. The 2.92mm connector has good electrical performance in the DC~46GHz frequency band and is mechanically compatible with SMA connectors and 3.5mm connectors. It is quickly recognized by the majority of manufacturers and has become the most widely used millimeter-wave in the world. One of the connectors.

Seeing this, it can be analogized to a 2.4mm connector, which is a connector with an outer conductor inner diameter of 2.4mm and an impedance of 50 ohms, while a 1.85mm connector is a connector with an outer conductor inner diameter of 1.85mm and an impedance of 50 ohms. Their inner diameter is smaller, so the operating frequency is higher, and the nominal frequencies can reach 50GHz and 67GHz, respectively. The two connectors are mechanically compatible and can be interconnected, but remember that they must not be connected to 2.92mm, 3.5mm or SMA connectors, otherwise it will directly cause the consequences of connector damage!

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