The Basics of Coaxial Connectors

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Coaxial devices are widely used in the microwave industry and are increasingly being used at millimeterwave frequencies up to 110 GHz. Because SAGE Millimeter’s products and services focus on higher microwave and millimeterwave frequencies, only miniaturized connectors will be discussed here. The following are concepts, terms and definitions that are widely used and accepted in the industry.

Coaxial Line:

A coaxial line is a transmission line that is comprised of an outer conducting metal tube that encloses and insulates an inner central conducting core. Coaxial lines are primarily used to transmit high frequency signals.

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Dominant Mode: The dominant mode of a coaxial line is the TEM mode. The electric and magnetic fields of the TEM mode in a coaxial line is shown on the right. Higher order modes tend to cause excessive loss. A coaxial line’s dominant mode of operation is governed by the diameters of its outer conductor (D) and inner conductor (d) and the dielectric constant (Ɛr) under the following relationship:Coax Formula 1

Characteristic Impedance:

                The characteristic impedance of a coaxial component operating within the TEM mode is given by:Coax Formula 2

Coaxial Connector Types:

The main coaxial connector types used in higher microwave and millimeterwave frequencies are summarized in the table below. “K” and “V” connectors are trademarks of Anritsu. Their alternative names are 2.92 mm and 1.85 mm connectors, respectively. “SMA” connectors are a trademark of Tyco Electronics, formerly known as Omni Spectra.

The inner diameter of the outer conductor “D”, the outer diameter of the inner conductor “d” and the dielectric constant of the connectors are provided below for various connector types. As shown in the table, the inner diameter of the outer conductor is used to name the connector type. For example, the 2.92 mm connector has an outer conductor with a 2.92 mm inner diameter. In addition, the indicated TEM mode operating frequency range for these connectors is wider than industry standard specifications. For example, the K connector’s operating frequency range is listed below as DC to 45.58 GHz, while the industry standard specification is DC to 40 GHz.

The Table:

The following table summarizes the most used coaxial connector types in SAGE Millimeter’s standard products. It gives the main characteristic of the connectors and the mechanical mate-ability between different types of connectors.

Chart

A PDF version of the chart can be found here.

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