Cables and connectors are continuously being created to fulfill the needs of todays applications while anticipating support for future needs.
In an ever-changing world, the cable market is a place where a company's expertise in one area can easily extend over decades. For example, W.L. Gore & Associates has been able to leverage its original work in polytetrafluoroethylene (PTFE) far beyond electronics. Think how many "new" cable assemblies are built with tried-and-true cable from firms like Times Microwave. Quality materials are being constantly refined to forge cables for new applications in telecommunications, medical electronics, defense, and broadcasting. Meanwhile, connectors are being forged with novel metal blends and improved machining processes. Together, these newly spawned cables and connectors offer high reliability and new levels of performance at ever-increasing frequencies.
At first glance, it may seem as if this market solely comprises the bigger companies. Yet a multitude of smaller companies have been created to fulfill unique and much-needed niches. To get a partial idea of the plethora of existing cable and connector companies, check out the lists of companies represented by distributors like RF Depot, RFMW, and Digi-Key. Although larger cable and connector companies invest more in research and development, smaller companies often contribute disproportionately to innovation.
According to Ruth Fawson, founder of RF Connections LLC and 40-year veteran of the connector industry, "We are entering a new era in connector and cable manufacturing. The technology leaders in connector and cable design have been swallowed up by mega-companies that are not always interested in supporting new development. That gap is being filled by new startup companies that have been created by the technologists who do not see their future in the mega-company environment. There is a tribal knowledge that was in danger of being lost. But in the new order, the emerging companies are protecting that knowledge and history, preserving the technical quality of available product."
Whether the demands of future applications will be best met by smallerand hence usually more agilecompanies remains to be seen. From the current landscape, however, it appears that this varied market offers opportunities to both the companies that want to leverage existing technology and those that have the desire and innovations to disrupt the traditional approaches with new technology. In the fiber-optic market alone, for example, cable and connector manufacturers have a strong revenue source.
Over the past year, active optical cables have garnered a significant amount of attention. According to Information Gatekeepers' recent Active Optical Cables Market Report, the total length of optical fiber shipped inside active optical cables is expected to range from 47 million meters in 2009 to nearly 1.1 billion meters by 2013. Total optical cables for vertical-cavity, surface-emitting-laser (VCSEL) system shipments across all speeds should range from 7.9 million units in 2009 to over 200 million units by 2013. The report emphasized applications with products using digital electronic interfaces running at or above 5 Gb/s as well as those demanding extended cable lengths beyond 2 to 5 m at those speeds.
The very-low-profile SFP+ directattach copper cable assembly from W.L. Gore & Associates is fiber-like in size while promising more flexibility than optical fiber (Fig. 1). The Low- Profile Copper Cable was designed to satisfy the needs of dense, higherport- count switch installations while providing a reliable interconnect for high-performance-computing (HPC) and networking environments using 10 Gigabit Ethernet, FCoE, or 8 Gigabit Fiber Channel. The cable uses a 2.10-mm round profile cable up to 2 m and a 2.80-mm round profile cable for 3 m.
This low-profile cable is targeted at data-center applications in which a large percentage of high-density portcount interconnects are 3 m or less. The cable is half the cross-sectional area of OM3 fiber-optic cable and one-third the size of 62.5/125-micron optical cable with a significantly reduced bend radius. By comparison, standard SFP+ copper cable assemblies in these lengths utilize cables that are roughly 4.40 mm in diameter and have a typical 30-mm bend radius.
Quellan, Inc. has been site sampling this Gore cable in active cable assemblies at 5-m lengths to various OEMs. With IU performance under 0.4, it is well below the 0.7 specification of the SFF-8431 standard. For its part, Quellan just made news with its release of active 6-Gb/s Mini-SAS copper cables, which promise to extend the reach of serial-attached-SCSI (SAS) interconnects to 25 m while enabling complete connectivity for data centers. During a live demonstration at the SAS Plugfest last November, active cables with lengths to 25 m interoperated with SAS devices from multiple storage drive and silicon vendors at the 6-Gb/s data rate specified by the new SAS-2 standard. In addition, cables to 30 m enabled communication at the legacy 3-Gb/s data rate.
This demonstration and product announcement follow the adoption of Quellan's proposed active mini-SAS specification by T10 (the body in charge of the development of the SAS standard) for inclusion into the draft of the upcoming SAS-2 revision of the standard. Active cables based on this standard will utilize the same mini-SAS connectors used in the passive interconnects. But they have provisions for an internal power supply as well as an active cable-detection mechanism to avoid short circuiting. The connectors provide keying features that prevent active cables from plugging into legacy passive receptacles while allowing active receptacles to accept both active and passive cables.
To satisfy communications applications ranging from optical to wireless, a plethora of cable types exist. According to Japan's Coax Co. Ltd., semi-rigid coaxial cable has more accuracy and consistency in construction than flexible cable. It therefore offers stable impedance matching and a low voltage standing wave ratio (VSWR). The company's Coax SC series of semi-rigid cable boasts a seamless outer conductor with shield characteristics like 120~130 dB to SHF range. Among the companies specializing in semi-rigid cable is RF Coax and Rosenberger, which promises repeatable performance in its semi-rigid cables for specifications to 67 GHz.
A family of hand-formable cable assemblies from Electronic Assembly Manufacturing, Inc. or EAM () promises to match the performance of semi-rigid cables (Fig. 2). These cable assemblies provide typical insertion loss of 0.7 dB/ft. at 20 GHz for a 0.141-in. diameter cable. VSWR is 1.13:1 at 18 GHz with capability past 20 GHz. These hand-formable cable assemblies minimize signal losses by means of a PTFE dielectric. To achieve shielding effectiveness beyond 100 dB, they incorporate a copper-tin-composite outer conductor. They can be easily bent into a desired shape without tools. Once they are bent, they will retain that form with minimal memory effects.
The cable assemblies are available in a range of standard and custom lengths with the same connector choices as semi-rigid cable assemblies.
The Conformable BJ cable family from Florida RF Labs offers a hand-formable replacement to semi-rigid cable with a metal foil under the copper-tin composite shield. From DC to 18 GHz, the cables handle power to 401 W at 1 GHz. They measure 0.047 to 0.141 in. in diameter while offering a minimum bend radius of 0.05 to 0.25 in.
In the defense and aerospace markets, the ability to withstand harsh environments ranks as high as power handling, VSWR, and other characteristics. For instance, M/A-COM's airborne electronic-warfare cable assemblies must successfully endure 29 torturous environmental tests before receiving the company's seal of approval. Test extremes include 65 G vibration, 65 to 200C at 70,000 feet, and 100,000 flexuresto name just a few. Another example is the fieldrepairable Iditarod coaxial cables from VMR Electronics, which are qualified for over 120 lbs. pull. Thanks to a very robust jacket, they claim to be resistant to abrasions and cuts.
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FORGING A CONNECTION
Compared to the material innovations behind cables, connectors seem like basic parts and are often overlooked. At 1 percent of the total cell-site material cost, for example, RF connectors are one of the least expensive items on a site. Yet these connectors provide the crucial link between all of the key components from radios to antennas. If one connector fails, the whole site's performance is therefore degraded. The AllTight RF connectors from PPC promise to provide a secure, reliable, water-tight connection for multiple types of corrugated, smooth wall, and braided cables.
The 50- AllTight connectors secure onto transmission cables at three specific points instead of just one. The company claims that the new Composite N receptacle offers the best compromise in terms of weight/cost/mechanical characteristics to replace existing brass technology. The connector boasts 100- percent compatibility with standard N brass connectors (MIL-STD-348-304). Yet it flaunts superior intermodulation performance with an input third-order intercept point under 115 dBm. The receptacle offers a VSWR to 1.13:1 at 6 GHz. Compared to brass, it provides a 50-percent weight reduction. The new AllTight connector is made with a typical metal RF insert to maintain the standard N dimensions and performance. It comes in a composite (plastic) outer body or corrosion-free housing offered in a variety of colors. The Composite N receptacle is guaranteed to 500 matings.
To satisfy base-station applications, HUBER+SUHNER has refined its QUICK LOCK mechanism for weather-exposed applications to create the first waterproof QMA solution. The QMA RF connectors are equipped with a QUICK LOCK locking mechanism instead of a threaded connection to save space and time while improving reliability. The new QMA connector interface vows to provide an SMA replacement below 6 GHz. The 50- interface covers DC to 18 GHz. It typically exhibits return loss above 32 dB from DC to 3 GHz and over 25 dB from 3 to 6 GHz. Passive intermodulation is rated at 120 dBc static at 1.8 GHz (tested with a pair of 20-W test signals). The interface offers IP68 ingress protection rating when mated. It is intermateable with QLFcertified standard QMA female. The interface boasts a 360-deg. rotatable interface and an enhanced temperature rating +105C. It is guaranteed for at least 100 mating cycles.
The connector arena often caters to already existing cables with "new" product releases or even offers replacements for discontinued connectors. For example, the RF Connectors Division of RF Industries () has released ultra-high-frequency male and female connectors for Andrew Corp.'s Heliax LDF4-50A 0.5-in. cable. These connectors utilize the same installation process and tooling required for the discontinued connectors. Manufactured with white-bronze-plated, machined brass bodies, they feature silver-plated phosphor bronze contacts and PTFE dielectric (Fig. 3). According to the company, white bronze is tarnish resistant while offering high conductivity and low intermodulation.
Harbour Industries' () LL142 cable has a new connector option from Precision Connector, Inc. Both male and female connectors are offered for the 2.92-mm (32 GHz), SMA (24 or 26 GHz), TNCA (18 GHz), and Type N (18 GHz) series (Fig. 4). The connectors feature solder/ clamp terminations and fully captive soldered center contacts. Straight, right-angle, and bulkhead configurations are available. The connectors employ both front and rear environmental seals for superior moisture resistance.
The apparent simplicity of connectors belies the machining innovations that allow them to support cable performance without hindering it. In fact, today's connectors provide long-term, dependable performance for a variety of applications as long as they are cared for correctly (see sidebar, "Properly Tend Coaxial Connectors"). They have evolved to couple with the various types of cables, such as flexible, semi-rigid, and conformable, that have emerged to enable applications ranging from high-speed optical communications to electronic warfare. Thanks to material developments and improved manufacturing processes, cables and connectors will continue to support next-generation applications. It is hard to tell at this point whether large or small companies will drive such evolution. But where opportunity emergesespecially in a tough economy savvy and innovative individuals will certainly be prepared to seize new opportunities.