The Basics of RF Coaxial Connectors

Updated: Nov 27, 2021

This blog post is sponsored by BUPAT GLOBAL LLC



Radio frequency (RF) coaxial connectors are electrical connectors that work with signals in the multi-megahertz range. They prevent outside signals from interfering with the information passing through coaxial cables. Before we get into connectors, first let's look at what Hertz, frequency and RF are.


Frequency is defined as the number of oscillations of a wave per unit time being measured in hertz, shown as Hz. If a device has a frequency of 50 Hz, it generates 50 electrical cycles in 1 second. If your heart beats at a frequency of 90 times a minute, its frequency is 1.5 Hz.


Wavelength is the distance between repeated units of a wave pattern. The wavelength is inversely proportional to the frequency, so the longer the wavelength, the lower the frequency. The unit of Wavelength is meter (m).


The frequency range between about 20 kHz and 300 GHz is called Radio Frequency (RF). Frequencies of 1 GHz and up to 30 GHz are conventionally called microwave (MW). In space, RF speed is equal to the speed of light.


The Hertzian waves (or electromagnetic waves) are the carrier waves that carry the signal (or information/data). RF and MW have the same behavior. The only difference is the frequency.


The coaxial line (co-axial = common axis) is an electromagnetic waves carrier. It is constituted of two metallic conductors held concentric by a dielectric. The coaxial connectors and cable assemblies are used in the transmission lines of many electronic systems for signal (or information) transport between different parts of the installation. These transmission lines are adapted to very high-frequency signal transport: RF and MW.


As the frequencies are very high, the electromagnetic waves are radiating a lot, and thus we must use this coaxial technology that encloses the waves into an envelope. The electromagnetic wave (the carrier that is transporting the signal) is flowing inside the dielectric (between two metallic conductors). There is always more loss into the dielectric (plastic = solid material) of a coax transmission line than in the air (permeability). That is why the coaxial transmission lines are always as short as possible.


A coaxial cable assembly is used for linking different parts of an installation. It is composed of coaxial connectors and coaxial cable. A coaxial cable assembly has two coaxial connectors assembled to a coaxial cable.


RF coaxial connectors are electrical connectors that work with signals in the RF range. They prevent outside signals from interfering with the information passing through coaxial cables. These connectors also enable signals to travel efficiently and reliably. RF connectors are used in a wide variety of applications, including antennas, Wi-Fi devices, radio systems, and more.


A coaxial connector has three main parts; the interface, body, and attachment.




INTERFACE


In the interface section, there are three models, two genders, and five coupling systems.


Models are plug, jack, and receptacle. The plug is the active part of the coupling system, while the jack is a passive part. The plug generally has a male center contact. The jack generally has a female center contact. These two are always fixed on a coaxial cable. A receptacle will have mounting features such as a flange with holes or a PCB mount, never fixed on a coaxial cable.



Genders are, as you can guess, male and female. A male has a male center contact called a pin. A female has a female center contact called a socket.





Some precision and measurement connectors have no gender, like the picture of Radiall's PC7 connector shown left. It is called a hermaphroditic connector.






The coupling system determines how you mate the same interface connector to each other. There are five main coupling systems; Screw-on, Snap-on, Silde-on, Bayonet, and Automatic Latching or Lock system, shown as below. We can also count a sixth one, the Press-on system.





BODY


In the body section, there are two shapes, and three fastening systems.


Shapes are straight and right-angle. The right-angle connector has a 90-degree angle with the axis for perfect mating in small gaps or tight places.




There are also U or Pi and T shapes. But they are not so common and only found in in-series adaptors.


For the fastening systems, there are three types. The bulkhead feedthrough connectors eliminate the fixing of cable assemblies. They are for panel jack and receptacle. The flange mount connectors can be square, rectangular, or round and have holes for fixing. They are also for panel jack and receptacle. The through-hole pins are used for the terminating leads of the connector and for mounting the connector to the PCB. Also exist in SMT and press-fit versions.



Independently of the chosen attachment technology, after the stripping operation, the center contact can be either soldered or crimped (= full-crimp)



ATTACHMENT


The attachment is the method that is used to assure the electrical contact between the cable braid and the connector ground contact, as well as the mechanical tightening of the connector on a coaxial cable, a single wire, a PC board, a microwave box, ...




The clamp type attachment





The crimp type attachment







The solder type attachment






Next, we will continue with the series of RF coaxial connectors with the support of Radiall, which offers the widest range of RF coaxial connectors in the industry. They offer over 13,000 part numbers and 55 product series, including AEP® and Mil QPL connectors. Stay tuned.



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