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RF Coaxial Connectors: A Simple Guide

TecTalk blog

RF connectors, also known as coax connectors, help transmit radio frequency signals by connecting transmission lines to various applications. RF connectors are mainly used with coaxial cables. You’ll find them used in TV receivers, two-way radio, Wi-Fi devices with antennas, and industrial and scientific measuring instruments. In this blog, we’ll cover some of the most common connectors including: BNC, SMA, SMB, N-type, and TNC.

RF connectors, while small, serve a larger purpose for coaxial cables. They need to match the specifications of the coaxial cable to reliably transmit the signal passing through it. So, having a general knowledge of coax connectors comes in handy when creating custom cable assemblies (or when requesting a custom assembly from a manufacturer). We’ve done the research and have compiled the most relevant information for you in this blog post. For a quick reference, download the RF/Coax Connectors Guide.

What is Coaxial Cable?

To better understand the function of an RF connector, we must first understand how a coaxial cable works. To send radio frequencies from point A to point B, we must use a transmission line. A coaxial cable is the preferred transmission line as it keeps the transmitted signal between the inner and outer conductors. This means a coax cable suffers less loss of signal and can be placed next to metal objects without any interference.

The diagram below shows that a coax cable contains: a center core (inner conductor), dielectric insulator, metal shield (outer conductor), and a jacket. The space between the inner and outer conductor is the impedance. This measurement is important to the function of the coax cable. The impedance must be the same throughout the entire length of the cable or it can result in signal reflection. When an RF connector is placed at the end of a coaxial cable, the impedance must match. Otherwise, the signal cannot be transmitted effectively.

What is a coaxial cable?

Common Types of RF Connectors

A well-designed RF connector blocks external signals from the circuit and prevents any loss of energy. These connectors have a built-in fastening mechanism such as thread, bayonet, braces, or blind mate. Important parameters to consider include: impedance, frequency range, power handling, size, and cost. Below we’ll cover some of the most common connectors in the industry today.

BNC (Bayonet Neill-Concelman)

The BNC connector features both a secure and quick fastening bayonet mechanism. It’s used with coaxial cable in radio, television, RF electronic equipment, test instruments and video signals. It’s available with either 50 ohms or 75 ohms of impedance. The frequency limit is usually 4 GHz, but can be greater if higher-quality versions are used.

BNC RF Connectors

 

SMA (Sub-Miniature A)

At about half the size of the BNC connector, the SMA connector is suitable for RF connectivity between boards, microwave filters, attenuators, mixers, and oscillators. SMA connectors have a threaded coupling which provides a secure connection. They’re available with a 50-ohm impedance and a frequency limit of 18 GHz.

SMA RF Connectors

 

SMB (Sub-Miniature B)

SMB connectors are even smaller than SMA connectors. They feature a snap-on fastening mechanism for quick mating and de-mating. These connectors are so small people specifically use them for inter-board or assembly connections within equipment. These connectors are available with either a 50 or 75-ohm impedance and have a frequency limit of 4 GHz.

SMB RF Connectors

 

N-Type

For a higher performance connector, you’ll want to go with the N-type connector. It is used for broadcast & communications equipment, power transmitters, receivers, and general RF applications. There are 50 or 75-ohm impedance options available. N-Type connectors also feature a threaded coupling mechanism. Although their 11 GHz frequency limit is lower than SMA connectors, precision versions can perform at up to 18 GHz.

N-Type RF Connectors

 

 TNC (Threaded Neill-Concelman)

Lastly, a threaded version of the BNC connector is the TNC connector. It’s available with a 50-ohm impedance and features a frequency limit of 11 GHz. The BNC connector bayonet fastening often introduces noise into the transmission signal. The TNC connector solved this issue. Hence, the TNC connector is able to perform at a higher frequency than the BNC.

 TNC RF Connectors

 

Selecting RF Connector Variations

Once you’ve decided on the type of RF connector, the next step is to determine which variations your application needs. Do you need a male or female connector? Straight or right-angled connector? The individual needs of your application will determine these decisions. Most applications will work fine with straight connectors, but you might opt for right-angle connectors if you’re tight on space. Right-angled connectors, however, suffer greater signal loss.

Whether you’re creating a custom assembly yourself or handing it off to an expert, we hope this has been useful in introducing you to the world of RF connectors. It’s important to note that these are only the most common connectors in the industry today. There are many more variations that we did not cover in this blog. If you’re looking for an experienced team to handle your custom RF cable assembly, contact us for a free quote.

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