SMA (Sub-Miniature-A) RF coaxial connector was invented by James Cheal of Bendix Company in the United States in 1958. It was used to solve the problem of TEM mode conversion between coaxial and microstrip because of its small size and structure. It has the advantages of simplicity, 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 has become the world’s most versatile RF connector with the largest variety of specifications and the largest amount of use. For this reason, its inventor won the World Microwave Application Award. SMA working frequency is 0～18GHz, suitable for 3～5mm soft, semi-flexible and semi-rigid cables.
SMA is developed for .141 (RG402) semi-rigid cable, so the inner conductor of RG402 coaxial cable can be directly used as the inner conductor of SMA — the transmission performance of this structure is very superior. SMA uses threaded connection, precision level It can be used up to 26.5GHz (the SMA developed by Yingkang Connector Co., Ltd. can be used up to 30GHz). Its maximum frequency is limited by the cable connected to it.
The advantages of SMA are high frequency, small size, and stable connection. SMA is widely used in the microwave field: coaxial cable to waveguide; coaxial cable to PCB microstrip. In amplifiers, attenuators, filters, mixers, SMA can also be seen in crystal oscillators and switches.
SMB (Sub-Miniature-B) RF coaxial connector is a push-in connector with a stopper. It was developed in response to the market’s demand for quick plug-in and unplugging of connectors. The center positioning function and overlap of the outer conductor shrapnel Insulators make SMB easy to snap and can maintain better performance in a vibration environment. It has the advantages of small size, convenient insertion and removal, good vibration resistance, and small space occupation. It is widely used in operating frequencies of 0-4GHz. Communication equipment, instrumentation and navigation systems, used in the connection of RF or digital signals between PCB boards and PCB boards…SMB has 50 ohm and 75 ohm versions, and some manufacturers’ 50 ohm SMB and 75 ohm It can be matched with each other, but some manufacturers are not.
SMC (Sub-Miniature-C) RF coaxial connector is similar in structure to SMB. It is a threaded deformation of SMB. Its internal structure size is the same as SMB. The operating frequency is 0～11GHz. The inner conductor and overlapping insulator structure are the same as SMB. Exactly the same, but the SMC uses a threaded connection mechanism instead of a snap form. The more precise control of the position of the inner conductor and insulator and the threaded connection structure allow the 50 ohm SMB to work at a frequency of 10 GHz. For the environment that requires small size and large vibration, SMC It is a good choice.
SMC is commonly used in microwave phones and non-military communication equipment, and is usually used in military equipment such as radar and navigation. Other ultra-small RF coaxial connector series include SMK/K (2.92mm), 2.4mm, 3.5mm, BMA (blind mating) ).
