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SMA connector
Monday, 20 November 2006

Subminiature series A (SMA) connectors are coaxial RF connectors to electrically join the inner and outer conductors of a coaxial cable to other electrical components such as a circuit board, a microstrip, a coplanar wave guide or to another cable. Coaxial cables comprise inner and outer conductors disposed in spaced concentric relationship with a nonconductive insulating material disposed uniformly therebetween. The inner conductor may be hollow or solid. At the end of coaxial cable, a connector is attached forming a coaxial cable assembly and facilitating mechanical and electrical coupling of the coaxial cable to electronic equipment and other cables. Coaxial cables typically are used to carry radio frequency or microwave frequency electrical signals. Coaxial connectors for radio frequency (RF) signals are typically used with a coaxial cable containing an external conductor/shield surrounding one or more internal conductors. The coaxial connector functions to align and provide an electrical path to the respective ends of the conductors while providing a continuous shield to minimize RF leakage. Coaxial cable has been increasingly used for certain microwave and other applications. Typically, the requirements for miniature coaxial cables have been governed by the military specification for coaxial connectors. The military designation for such miniature coaxial connectors is SMA (Subminiature Series A). Subminiature coaxial connectors are used with microwave active and passive components, high-end radio electronics, instrumentation applications and avionics. SMA connectors are advantageous because they are inexpensive, possess high mechanical strength, and are easy to probe.

SMA connectors perform their signal carrying function very well and are employed widely throughout the telecommunication, computer and home entertainment industries. Subminiature coaxial connectors are operable at broadband frequencies and have low reflections. They are typically designed to have a constant 50 ohm impedance and are constantly used in many applications where an interface must be made from a coaxial line to a trace or other circuit element printed or otherwise positioned on a circuit board. A typical SMA connector assembly includes one connector with an externally threaded outer shell formed from a metallic material that forms a part of the ground or shield around the connector. The opposed connector has a metallic lock nut with an array of internal threads. SMA connectors essentially comprise a male connector consisting of a conductive pin extending from the center of a dielectric plug and a female connector consisting of a sleeve which receives and makes electrical contact with the pin. SMA connectors generally include a center pin having a tab on its inner end and a female recess on its opposite end. The center pin is surrounded by a Teflon insulator which serves to support the center pin in the outer housing. The housing acts as the outer coaxial conductor around the center pin. Standard SMA connectors utilize a threaded coupling or locking nut as the locking mechanism to connect the male and female connectors. The lock nut is engaged threadedly with the external threads on the shell of the mating connector and also is connected to the outer conductor on the cable. SMA connectors provides a male pin having a diameter of 0.036-0.037 inch. The female socket to which this male pin will be mated typically will have an external dimension of only 0.0495-0.0505 inch.

Subminiature coaxial connectors are commonly used as high performance subminiature connectors at microwave frequencies. Subminiature connector assemblies are generally utilized to connect a cable, such as a coaxial cable, to circuit boards. Such connectors are commonly referred to as SMA, SMB or SMC connectors to designate operation of the subminiature connectors in different frequencies. Sub-miniature series A connectors are often used to couple the coaxial cable to the stripline conductors. Microwave signals are often carried on shielded coaxial cables. These cables are typically used to transmit microwave signals to and from various end devices. Many of these end devices require that connections to them are made by way of flat or "stripline" conductors residing on a surface of a dielectric board. SMA (subminiature series A) connectors are sometimes used to couple time domain reflectometer (TDR) equipment to the circuit board for testing. TDR is the industry-standard tool used for circuit board impedance measurements. Subminiature coaxial connectors operate at broadband frequencies and have low reflections. Because are designed to have a constant 50 Ohm impedance, making them advantageous for use in various applications in the microwave industry. SMA connector is available both in standard and reverse polarity forms. Reverse polarity SMA connector is accomplished with a reverse interface to ensure that reverse polarity interface connectors do not mate with standard interface connectors.