by Amar Ganwani, Sr. RF Product Manager, Fairview Microwave
Coaxial cables and connectors are remarkable feats of electrical, electromagnetic, and mechanical engineering designed to accommodate the vagaries of electromagnetic energy. They must have the lowest possible insertion loss and VSWR, high phase and amplitude stability, the ability to maintain their performance over wide temperature ranges with high resistance to ingress of external signals, and other capabilities. But in service they don’t have an easy life. They’re subjected to harsh conditions and abuse, such as exposure to extreme temperatures, immersion in chemicals and fuels, and exposure to salt water, among other environmental factors.
However, the most prevalent cause of cable and connector failure is actually handling and installation. A recent survey noted that the most frequently cited reason for failure was damage during mating and unmating. It’s arguable that they also suffer when they’re used as a convenient way of moving a test cart from one place to another. The study also noted that at least three-quarters of microwave cable assemblies are replaced frequently, 36% are replaced once a year, and 20% are replaced at least twice a year.
The damage is rarely intentional, but installers, unlike their creators, know little about microwave cables and connectors, which is fine in the consumer world where cables and connectors are commodities, generally inexpensive, and expendable. But in defense, aerospace, and other mission-critical applications failure is not only costly but potentially catastrophic.
It’s important to educate those who install these cables and connectors about best practices for handling, installation, and maintenance, including not to kink, bend, or step on the cables, how to properly mate connectors with recommended torque, and how to store and transport cable assemblies. Quality connector installation tools, such as precision torque wrenches, are also a necessity, as is the need to make sure everyone uses them.
That said, it’s not reasonable to expect everyone who encounters high-frequency cables and connectors to understand how they work, but a case can be made that they should know that these fragile components must be handled with care, not only because mishandling can have disastrous results, but because they are expensive to procure and extremely costly to replace once installed.
Manufacturers have made great strides over the years to make these components as rugged as possible without significantly increasing their cost. Some of the most important advances are resistance to kinking, crushing, or bending beyond the recommended minimum bend radius.
However, as defense and commercial systems increase in frequency, connector manufacturers are faced with developing products that can operate there, balancing performance and reliability with minimizing their size and cost. The size reduction can be a challenge for manufacturers as these smaller components become more delicate and difficult to handle.
The latest advances in connector technology include the realization of an astonishingly small 0.8-mm connector body by Anritsu that operates mode-free to 145 GHz (and possibly higher) at an equally astonishing cost. The 0.8-mm connector has an air dielectric front-side interface like lower-frequency K and V connectors, with the center conductor supported by a proprietary, low-loss support bead on one end and a PTFE bead on the other. The question for test equipment manufacturers now is how to make these connectors rugged in order to meet the challenges posed by vector network analyzer testing that involves repeated mating and demating of connectors and cables.
Neither DoD nor the wireless industry is demanding connectors at the 0.8 mm level or smaller as of yet, so the industry at least has time to innovate and find solutions to this challenge. This includes, for example, finding new methods of connecting or new materials that can withstand high-frequency signals while also maintaining high performance over hundreds of mating cycles. It will not be easy, but whenever there has been a need, the industry has consistently found a way to achieve a solution.
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