Development and Limitations of SMA Connectors

The SMA (Sub-Miniature-A) the radio frequency coaxial connector was invented by James Cheal of Bendix Company in the United States in 1958. Due to its small size and structure, it was used to solve the problem of TEM mode conversion between coaxial and microstrip. It has the advantages of simple structure, wide operating frequency, and high reliability, so it will soon be widely used in aerospace systems, microwave communication engineering, and military weapons.

At present, SMA connectors have become the most widely used RF connectors in the world. For this, its inventors received the World Microwave Application Award. The working frequency of SMA is 0-18GHz, suitable for 3-5mm soft, semi-flexible, and semi-rigid cables. The SMA was developed for 141 (RG402) semi-rigid cables, so the inner conductor of the RG402 coaxial cable can be used directly as the inner conductor of the SMA - the transmission performance of this structure is very superior.

The SMA is threaded and has an accuracy class of up to 26.5GHz. Its maximum frequency of use is limited by the cable it is connected to. The advantages of SMA are high frequency of use, small size, and stable connection. SMA is widely used in the microwave field: coaxial cable to waveguide; coaxial cable to PCB microstrip line. SMAs can be found in amplifiers, attenuators, filters, mixers, crystal oscillators, and switches.

SMA connectors operate at 22GHz. It is not a millimeter wave connector, but it has had a great influence on the development of millimeter wave connectors. The matching space of SMA is filled with polytetrafluoroethylene medium, and the structure is relatively simple. This connector is not intended for long-term use, nor is it considered a precision connector. Therefore, SMA connectors are just common system connectors.

In this case, due to the small size of the SMA connector and the ability to work at a higher frequency, it quickly became popular, and even when a new generation of millimeter-wave coaxial connectors was developed later, they had to consider connecting with SMA device compatibility issues.

However, the inherent deficiencies of SMA connectors also brought certain restrictions to the development of small coaxial connectors. The main problem of SMA is that the accuracy is not high, and it is not suitable for the needs of test equipment; the second is that the outer conductor wall is thin, and the inner conductor socket has a double-slot structure, which is extremely easy to wear and damage during use. Secondly, the working frequency is not high, which cannot meet the system requirements of the working frequency band above 40GHz.

Due to these shortcomings of SMA connectors, some manufacturers have developed some SMA-compatible connectors, the main models are 3.5mm, WSMA, and later developed 2.92mm, MPC3, KMC, and WMP4. These connectors overcome the limitations of SMAs and are structurally different from SMAs. In terms of the contact area of the outer conductor, the newly developed connector is greatly strengthened, improving the sturdiness of the connector.

The above briefly introduces the development and limitations of SMA connectors. If you want to buy SMA connectors, please contact us.

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