As demands on system performance increase, cables, connectors, and cable assemblies are using new materials and techniques to increase accuracy, repeatability, and flexibility while reducing size and weight.
Compared to whiz-bang radios and other flashier RF products, cable and connector development seems relatively slow. Yet the companies that produce cables, connectors, and cable assemblies are continuously developing new products. In the connector arena in particular, the last six months have seen a rising number of product introductions to meet the needs of emerging military, aerospace, test and measurement, and other applications. Today's cables and connectors strive to satisfy the omnipresent demands for size and weight reductions with improved electrical performance. In addition, the test arena has been teeming with cables and connectors designed as accessories for vector network analyzers (VNAs).
Part of this pressure is stemming from the fact that the industry has become well educated in its cable and connector needs. According to Steve Baldo, Global Business Leader for Test & Measurement Products at W.L. Gore & Associates (Elkton, MD), "Today's customers are better informed about the various aspects that affect a cable assembly's performance and life cycle, such as phase and amplitude stability, repeatability, phase matching, low loss, and ruggedization/service life. Aside from wanting higher-performing cable and connectors, the industry wants everything smaller with higher-density solutions—especially in the defense, space, and automated-test-equipment (ATE) markets."
In response to the trend toward smaller products with better performance, Insulated Wire or IW (Danbury, CT) developed a line of lighter-weight coaxial cables and assemblies with smaller diameters, lower insertion loss, and enhanced electrical stability compared to temperature and flexure. The line combines silver-plated copper conductors with low-loss, expanded polytetrafluoroethylene (PTFE) dielectric. The line's RF leakage characteristics are specified at >-100 dB to 18 GHz. The 1801 product, for example, has a diameter of 0.185 in. with a bend radius of 1 in. Its maximum frequency is 34 GHz.
For those customers who are calling for flexibility and cost savings during the early stages of design but with the performance levels of semi-rigid cables, Emerson Network Power Connectivity Solutions (Bannockburn, IL) recently released a line of hand-formable cable assemblies. These assemblies eliminate additional tooling charges. In conjunction with the company's Johnson brand of connectors on each end, these SMA hand-formable cable assemblies are constructed of silver-plated, copper-covered steel conductor with an additional copper-tin composite braid foil (Fig. 1). When RF interference isn't an option, the cables provide 100-percent shielded cable coverage, which assures a superior voltage standing-wave ratio (VSWR) and low insertion loss of up to 18 GHz. For example, the 415-0081-003 offers a nominal delay of 0.36 ns. Its insertion loss versus frequency is 0.41 dB/ft. for 6 to 12 GHz. At 1 to 2 GHz, the maximum VSWR versus frequency is 1.10:1. The assemblies are available in a variety of off-the-shelf and custom lengths with a diameter of 0.086 or 0.141 in.
Many recent performance-enhancing products were spawned by the military sector. In the cable arena, for example, Semflex, Inc.'s (Mesa, AZ) SLA series microwave cable offers low attenuation to target phase-critical applications like radar and ECM. This feat is accomplished with the use of silver-plated inner and outer conductors and microporous dielectric PTFE material. Low loss, phase stability, and shielding effectiveness of >100 dB result from combining a helically served flat braid with a second shield of 97-percent minimum-coverage round braid. Additional performance characteristics include low loss of 19.5 dB/100 ft. at 18.0 GHz with superior phase and temperature stability.
Obviously, such improvements stem directly from material advancements. These types of developments-will certainly continue, as many companies are steadily investing in materials. This month, for example, Micro-Coax (Pottstown, PA) announced the acquisition of ARACON-brand metal clad fibers. The ARACON fibers are a lightweight, high-strength alternative to conventional metal wire. The fiber is produced by applying a patented metallization process to a base Kevlar fiber. The resulting conductive fiber offers significant weight savings and enhanced RF shielding properties. It is well suited for aircraft wiring overbraids and other aerospace applications in which weight and reliability are critical.
Ted Worroll, Product Manager for the Americas at ITT Electronic Components (Watertown, CT), predicts that the near future will see the use of plated plastics within the connector high-frequency offering, lower-loss cables, and combination-series connectors including RF, low-frequency (LF), fiber, and power. In keeping with these trends, ITT's switchable RF connector combines miniaturization with durability and high performance. The MINI RF series supports signal frequencies up to 6 GHz (Fig. 2). It incorporates 3-deg. misalignment, thereby allowing for angular misalignment when mating sections are engaged. With the contacts sandwiched between two insulators, the design minimizes the risk of solder flux switch contamination. Beryllium-copper contacts are used with insulators made of liquid-crystal polymer. The shell is copper alloy (phosphorous bronze) with an additional layer of matte tin or gold-over-nickel for the test-port or accessories-port versions, respectively. The MINI RF series measures just 2.7 x 2.7 mm with a height of 1.6 mm high. The connectors' snap-on interface allows for 100 mating cycles.
Companies also are nurturing the evolution of cables and connectors by re-applying existing design techniques. For example, HUBER+SUHNER's (Essex, VT) SMART QUICK-FIT connector range brings a mechanical solution to the design of high-performance RF connectors for the termination of corrugated copper feeder cables. The new connector family will typically be used for feeder-line systems of radio transceivers—especially mobile-phone-network base stations. The series targets 7/8- and 1/2-in. corrugated-foam dielectric cables. The connectors can be used with HUBER+SUHNER's cables as well as most other cable brands. The waterproof (IP68) connector comes with a unique stripping tool that fits most types of cables in the market. The new connector offers a two-piece design with DIN 7/16 and Type N interfaces.
By leveraging a unique system of sealing, another connector line promises to remain waterproof inside and out. The connectors, which hail from Radiall (Chandler, AZ), don't rely on the usual approaches of soldered hermetic seals or separate caps. Yet the company's sealing system promises to offer electrical performance comparable to the performance of hermetically sealed connectors. The connectors are available as receptacles with many contact termination styles, cable connectors (with either clamp or crimp-type cable attachment), or adapters.
New crimp connectors for low-loss LMR-400 cables from Times Microwave Systems (Wallingford, CT) and Belden 9913 cables are now available from RF Connectors, a division of RF Industries (San Diego, CA). Depending upon the coaxial cable used in the assembly, the BNC—dubbed the RFB-1106-I—is designed to perform to a minimum of 4 GHz. The TNC connector, which is called the RFT-1202-I, was created to perform to a minimum of 7 GHz (Fig. 3). Both connectors feature gold-plated contacts that can be soldered or crimped. They also boast Teflon insulation and nickel-plated brass bodies.
Such connectors are an essential part of cable assemblies. After all, cable assemblies are simply cables with crimped connectors soldered onto them. Yet the plethora of choices, materials, and specifications can make it difficult for an engineer to pick the right assembly for his or her application. To aid this process, W.L. Gore & Associates just launched the GORE Microwave/RF Assembly Builder. This online tool builds on the company's high-flex flat and trackless cable configurator, which was launched last year. The GORE Microwave/RF Assembly Builder is an interactive design guide. It strives to simplify the assembly design and configuration process by enabling the user to build an assembly and submit an RFQ using the simple step-by-step configuration tool. No registration is required to access this process. To try out the new configurator, go to www.gore.com/rfcablebuilder.
Although the world of test is often considered secondary for cable assemblies, this application area is driving a great deal of cable and connector development. As Gore's Steve Baldo emphasizes, "Test and measurement equipment, such as vector network analyzers, have correspondingly increased performance capabilities with systems that are standardly available through 110 GHz. Stability and repeatability of the cables and connectors becomes extremely important in such sensitive applications." Gore's PHASEFLEX 110-GHz test assemblies offer torque and crush resistance and stability with flexure and temperature (Fig. 4). In addition, they can be flexed, reformed, or repositioned. For example, an assembly was bent 90 deg. around a 1-in.-radius mandrel. Yet there was only 4.3 deg. and 0.05 dB change at 110 GHz. When the assembly was returned to its original configuration, phase and amplitude returned to their original values. As far as electrical performance is concerned, a 10-cm-long assembly offers typical loss of 1.34 dB, guaranteed loss of 1.74 dB, and VSWR of 1.50:1. Impedance is 50 ohms.
The Synflex test line from Synergy Microwave (Paterson, NJ) comprises two product families. The SF Series, which spans DC to 18 GHz, has a solid silver-plated, copper-clad steel inner dielectric. The dielectric is solid PTFE. In contrast, the SFR Series covers DC to 8 GHz. It has a stranded silver-plated inner conductor and PTFE dielectric. The connectors offer a gold-plated, brass-center contact and a passivated stainless-steel coupling nut. They also feature captive contacts and PTFE dielectric.
Although M/A-COM (Lowell, MA) usually garners attention for its military, space, and RF cables and connectors, the company also has a noteworthy line of general-purpose test cables. To deliver optimal performance, these durable test cables offer numerous mix-and-match options. For example, customer-replaceable interfaces allow a single cable to interconnect a variety of male and female interfaces without degrading the low loss and VSWR of the cable assembly. In addition, the outermost layer of these cables may be extruded FEP (for FC-type cables) or extruded polyurethane (FE type). For more severe environments, the extruded FEP layer is covered with overlapping layers of adhesive-backed Polyimide tape, which is used as a vapor barrier. It is then covered with weave Nomex, which is saturated in Polyimide to prevent fraying.
The FNxxG-type test cable is jacketed with green-tinted Nomex. It will survive very severe abrasive conditions—similar to those required by MIL-T-81490. A range of connector-interface styles is available for these cable types. They all promise to provide low VSWR and superior cable-connector retention characteristics. In addition, the critical cable/connector junction is reinforced with a tapered, molded,bend-restricting boot that prevents damage when the cable is bent.
A range of test cables and connectors also hails from Mini-Circuits (Brooklyn, NY). The 50-ohm Flex test cable assemblies all provide wideband coverage from DC to 18 GHz. The assemblies boast high stability of insertion loss, VSWR, and phase versus flexing. At 12 to 18 GHz, for example, the CBL-1.5FTSMSM+ offers 1.0 dB typical and 1.4 dB maximum insertion loss. Its return loss is 27 dB typical.
In addition, intermodulation testing and measurements can now be handled by the 50T-453 RF load from JFW Industries (Indianapolis, IN). It offers -165 dBc at 1950 MHz with two 20-W tones. The RF load boasts a 50-W input-power rating and a low VSWR of 1.20:1 maximum at 3000 MHz. It is available with 7/16 or N connectors.
In summary, cables, connectors, and cable assemblies are being pushed to new performance heights whether the driver is telecommunications, military, test, or another application area. At the same time, they are shrinking and becoming more compact, flexible, and rugged. As new materials are developed—in addition to new applications of existing materials—such improvements will continue to birth technology advancements. For a more complete listing of cable, connector, and cable-assembly providers, please visit the Microwaves & RF Product Data Directory at www.mwrfpdd.com.
