There are many kinds of radio frequency connectors , in order to meet the needs of various frequencies and physical structures. People have designed a variety of connector types, with each type of connector is required to meet the corresponding connector standards.
The frequency range of the coaxial connector is limited by the first-order round waveguide mode. Reducing the radius inside of the outer conductor can correspondingly increase the application frequency range, and the operating frequency can be reduced by adding a dielectric material, while also increasing the insertion loss of the connector.The performance of the connector is greatly affected by the quality of the contact surface.If the radius of inner conductor and outer conductor is slightly different from the design value, the connection node will be separated, which will increase the port reflection coefficient and lead to large transmission loss. Therefore, the connector machining accuracy will be higher and higher with the increase of application frequency.
This article will focus on the SMA Connector mainly, which is the most widely used in RF circuit design. The typical SMA connector support frequency DC-18GHz , there are some high precision types can support up to 26.5GHz too.
In fact, SMA and 3.5mm (Up to 34GHz),2.92mm (or K connector, up to 40GHz), both 3.5mm and 2.92mm refer to the coaxial inner diameter of the outer conductor, SMA connectors have foam beads, while 3.5mm and 2.92mm connectors use air interface.On the mechanical structure, these three connectors are compatible, that is to say the three connectors can be directly connected with each other. But due to the frequency differences, the higher the frequency, the better the performances on mechanical tolerance, stability, temperature, SWR, repeatability, loss and coating. It means high-level joint damage will be caused when different standard joints are connected with each other. It is strongly recommended to avoid frequent connection of different types of connectors.
Connector appearance drawing and dimensions
|Connector Type||Frequency Range||Compatible type|
|2.92mm||to 40GHz||3.5mm and SMA|
|3.5mm||to 34GHz||2.92mm and SMA|
|SMA||to 24GHz||2.92mm and 3.5MM|
The improper operation can cause damage to the connector, affecting the measurement results and service life.
Do not connect incompatible RF joints by force.
When connecting RF joints, please note that the female head must not be rotated. The correct operation is to rotate the male threaded housing. This helps to reduce the wear between the inner core and the probe, and prolong the service life of the device.