Interconnection
The engineer’s guide to RF cable assembly selection and use
By Rolf Horn, applications engineer at DigiKey R
F cable assemblies are used in a wide range of applications, from well-established domains like aerospace and communications, to newer use cases like
automotive, industrial, and the Internet of Things (IoT). This expanding list of applications has prompted the development of new types of RF cable assemblies, giving engineers further opportunities to optimize their RF system designs.
However, all this growth is complicating the design process. With so many assemblies on the market, it is difficult to identify the best choice for a particular application. Also, the use of RF cabling in new applications is putting unfamiliar technology in front of more designers, installers, and maintenance technicians. Along with space and environmental considerations, those groups must now become familiar with frequency compatibility, impedance matching, voltage standing wave ratio (VSWR), magnetic coupling, and shielding.
To ensure the performance and reliability of RF systems, engineers need an attentive approach and a clear roadmap of the options and potential pitfalls that await them. Beginning with a brief overview of RF applications including their electrical characteristics, physical construction, and typical use cases, this article serves as a guide to the complex task of choosing, installing, and maintaining RF cable assemblies. Examples from Molex are introduced to illustrate key selection and usage criteria.
The expanding use cases of RF cable assemblies
RF technologies span a multitude of sectors, each with its unique challenges. Frequencies range from hundreds of hertz (Hz) to tens of gigahertz (GHz). Some applications require ruggedization. Others have extremely confined physical footprints. To illustrate the diversity of use
46 March 2024
Figure 1: RF cable assemblies come in a wide variety of designs, which can be categorized by the size of the connector and their maximum supported frequency, among other factors. (Image source: Molex).
cases, consider these common applications:
● Aerospace and defence: Radar systems, communication channels, and GPS
● Automotive and transportation: Infotainment systems, navigation, and vehicular communication networks
● Telecommunications and broadcast: 8K video signals over Wi-Fi, LTE, and 5G networks
● Industrial: IoT sensors, automated assembly lines, and telemetry
● Medical: Remote patient monitoring systems, advanced diagnostic machinery, and robotic surgery units
● Test and measurement: Bench measurements, field tests, and quality assurance in manufacturing setups Due to the growing use of RF, more engineers and designers are engaging with high-frequency circuits, many without a
Components in Electronics
background in this technology. Faced with tight deadlines and budgets, they need solutions that simplify their tasks while ensuring their systems perform reliably. That is where RF cable assemblies come in. These assemblies consist of pre- assembled connectors and cables that meet the specified performance requirements while reducing the engineering effort. Using premade RF cable assemblies can save time and cost during design and prototyping, and improve the quality and efficiency of production.
Frequency compatibility, impedance matching, and VSWR
Choosing the appropriate cable assembly requires careful consideration of multiple factors. First, the assembly must be able to accommodate the frequency range of the RF
signal. These can vary from a few hundred hertz to the super high frequency (SHF) band of 3 to 30 GHz or higher (Figure 1). To achieve the desired performance, a cable assembly must handle the appropriate frequency range without significant signal loss or distortion. For example, the Society of Motion Picture and Television Engineers (SMPTE) sets stringent signal quality requirements under their 2082-1 guidelines, which limits loss to 40 decibels (dB) at half the clock frequency.
One way to meet these demands is with the Molex BNC Mini RF Cable Assemblies, which deliver high return-loss performance at frequencies of up to 12 GHz. This performance exceeds the requirements for serial transmission of 8K high-definition TV (HDTV) video, allowing for future bandwidth expansion without hardware changes.
www.cieonline.co.uk
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