Transmission-line components have evolved in composition, performance, and form to support wireless-communications systems and other modern-day technologies.
Transmission-line components are certainly not the flashiest part in a wireless system. Yet they are an essential part of this market's backbone. These components serve a variety of segments ranging from commercial and consumer to military and base stations. In doing so, they take many forms ranging from raw cables and individual connectors to complete cable assemblies. The companies that provide these products are numerous and many of them overlap in the different product areas. All of them are similar in that they are striving to satisfy their customerswireless and otherwiseby developing new, innovative components.
The cable market in particular is quite varied in its offerings. Cables vary in features like material composition and flexibility (or lack thereof). In addition, they come in a plethora of sizes and forms. The LMR cables from Times Microwave Systems (Wallingford, CT), for example, are available from LMR-100 (0.100 in.) all the way up to LMR-1700-DB (1-1/4 in.). This product line was specifically designed for the wireless-communications market. Although the cables' RF performance is comparable to traditional corrugated copper cables for antenna feeders and system interconnects, they are highly flexible and non-kinking. This flexibility makes it possible to eliminate jumpers in many feeder-cable applications. The LMR cable includes polyethylene foam dielectric, a high-performance flexible shielding system, and multi-laminar aluminum composite tape bonded to the dielectric. It provides >90 dB isolation shielding (180 dB crosstalk). LMR connectors and other accessories are available as well.
The Mobile Solutions 2 (MS2) cable family from Thermax (Whitestone, NY) features an air-spaced PTFE dielectric that provides low loss while saving weight. The sophisticated double shielding virtually eliminates crosstalk. In addition, the dielectric construction and extruded FEP jacket ensure consistent performance throughout the cable's extended temperature range. Five products are currently available under the MS2 banner. The specifications for the MS2-110 include a temperature rating to 200C, impedance of 50 2Ω and 26 pF/ft. capacitance. In decibels per 100 ft., the cable's attenuation is 14.3 at 500 MHz; 20.7 at 1 GHz; 36.4 at 3 GHz; 47.0 at 5 GHz; 69.0 at 10 GHz; and 96.5 at 18 GHz.
The wireless market also is the main target of the AirCell cable from Trilogy Communications, Inc. (Pearl, MS). Trilogy just recently sold the assets supporting its 75-Ω CATV Trunk and Feeder Coaxial business and certain other assets to CommScope, Inc. of North Carolina. Trilogy will now funnel its energies into the wireless market by continuing to manufacture and market its AirCell product line. The wireless coaxial product line includes the Air-Cell Transline for tower/base stations, AirCell Radiating for tunnels/metros, and AirCell Plenum for the inbuilding market. The AirCell cables were recently chosen for use by Heathrow Airport, London, and Beijing Metro projects in China.
Of course, CommScope (Newton, NC) is a wireless player in its own right. Among the company's product lines is Extremeflex, which is the aluminum-cable improvement of its Wireless Transmission Line System. Compared to traditional corrugated-cable systems, this 50-Ω aluminum-cable design promises to deliver superior performance, reliability, and lower life-cycle costs over the life of a wireless network. Impressively, the Wireless Transmission Line System claims to have eliminated any need for secondary weatherproofing as long as cables and connectors are properly installed. The smooth-wall cable and connector design is intended to eliminate water ingress. The Comm-Scope system survived over 150 tests including temperature cycling from -40 to +60C, constant rain simulation up to 27 in., and ice spray at -5C.
For an alternative to semi-rigid cable offerings, check out the Re-Flex Cables from Insulated Wire (Danbury, CT). They feature a laminated polytetrafluoroethylene (PTFE) dielectric, dual tinalloy foil shield, and tightly woven copper braid. These aspects give it the same leakage characteristics as semi-rigid cables. The Re-Flex cables can be easily formed into position by hand and then reformed without electrical or mechanical degradation. The non-solder-coated design vows that it will not fracture under vibration or stress. The Re-Flex cables can be purchased alone or as assemblies with SMA straight-plug connectors in lengths of 2 to 18 in. The Re-Flex connectors claim that they will not break free from the cable under adverse conditionsa problem that has been witnessed in other flexible, semi-rigid connector alternatives.
The microbend cable-assembly family-from Astrolab (Warren, NJ) also is designed to replace semi-rigid cables and connectors. These products are billed as standard, preassembled, flexible alternatives to 0.047-in. custom, semi-rigid cable assemblies. Their features include a minimum bend radius of 0.060 in., triple shielding for high isolation, a protective FEP jacket, and a frequency range of up to 65 GHz. They are available with the following connectors: 1.85-mm plug, SMPM female, SMP male and female, 2.9-mm plug, and SSMA and SMA plug. These products hail from the company's minibend connector-assembly line, which has multiplied to offer solutions for a plethora of communications and military applications.
Many companies offer a mix of flexible and semi-rigid options. An example is Storm-Microwave (Santa Monica, CA), which provides interconnect solutions for the wireless market ranging from the base station to the antenna. This company also is highly active in the telecommunications and defense and aerospace arenas. Its Phase Master microwave-cable assemblies target phase-sensitive applications. These lightweight, flexible, 0.190-in.-diameter assemblies boast nominal attenuation of 0.110 at 2 GHz (dB/ft.), 0.260 at 10 GHz (dB/ft.), and 0.360 at 18 GHz (dB/ft.). At 1 GHz, their average power is 700 W. The assemblies' Micro-Form construction requires less-frequent calibration because of its flatter phase-versus-temperature profile. Compared to flexure, it promises more precise measurements because of its reduced phase shift. It also claims to provide reduced insertion loss and increased amplitude stability. Robust connector attachment/captivation and crush-and kink-resistant armoring options round out these assemblies.
To satisfy applications that bridge the wireless and defense arenas, such as mobile battlefield communications, Trompeter (Mesa, AZ) has released a multi-interconnect shielded-cable assembly. Dubbed the MDM Octopus, it features multiple twinax or triax RF connectors and a single Microminiature-D-Metal (MDM) multipin connector. The twinax and triax connectors are terminated on one end while the multi-pin connector is terminated on the opposite end (Fig.1). The MDM Octopus provides a densely packaged, multi-pin interconnect that doubles as a lightweight shielded assembly. Its metal backshell replaces the traditional molded-polymer-backshell approach to managing multiple interconnects in tight spaces. The result is a more secure electrical EMI/RFI ground and combat-ready package. The MDM Octopus is compliant with MIL-DTL-83513.
Of course, wireless communications and defense/aerospace are just a small representation of the applications that require transmission-line components. In the electronics industry, many cable-centric companies are heavily invested in the test and fiber-optics markets as well. There is some overlap between their specialties and wireless-communications cable applications. Last year, for example, NextG Networks (Milpitas, CA) began merging the benefits of wireless and fiber-optic communications by using distributed antenna networks to deliver RF to targeted areas. The company is giving wireless carriers and service providers a fast and economical way to enable service where coverage holes, capacity limitations, and restricted access left consumers under-served. NextG has chosen cable-providergiant Corning Cable Systems, part of Corning, Inc.'s Telecommunications segment (Corning, NY), as its national fiber-optic cable and hardware supplier.
Making The Connection
When it comes to connectors, some manufacturers specialize solely in this component area. For the most part, however, cable and cable-assembly makers also deal in connectors.
Corning Gilbert, for example, offers a myriad of connectors for both the broadband and microwave arenas. Its "F"-series connectors permit a coaxial cable to maintain a 75-Ω impedance. These connectors are used with the 59, 6, 7, and 11 cable series. The UltraSeal and Ultra-Ease series of compression connectors boast low activation force in a high-performance compression connector. They promise to deliver superior RF shielding integrity and a complete seal to the cable jacket, thereby locking out moisture.
Astrolab, Inc. (Warren, NJ) designs and manufactures RF and microwave coaxial connectors for applications up to 65 GHz. Tensolite (St. Augustine, FL) also offers a robust line of connectors. This company recently introduced a new connector series with the same footprint as a standard-size 1 through 4 D-Sub. The RF-DSUB series promises up to a 50-percent increase in high-frequency RF-signal density with performance from DC to 40 GHz.
Another active participant in the connector arena is Huber+Suhner. This company just won an order for RF assemblies and connectors for the second series of 2376 Eurofighter Typhoon aircraft. The RF components will link the system's antennas, computers, transmitters, receivers, and other components that constitute the aircraft's Defensive Aids Sub System (DASS).
The Coax Surface Mount MID (CoS-MID) 75-Ω connectors from ITT Electronic Components (White Plains, NY) use molded-interconnect-device technology to integrate two, three, or four coaxial connector lines into a single surface-mountable module (Fig. 2) . As a result, both sides of the printed-circuit-board (PCB) card edge can be used. The four-line modules can be configured in a stacked 2 X 2 formation, which again doubles the line density. The 50-Ω SMA-connector range from ITT comprises straight and right-angle plugs and jacks for flexible coaxial cables, 0.141- and 0.085-in. semi-rigid and conformable cables, and PCB and flange-mount variants. These connectors promise to provide superior electrical and mechanically durable performance from DC to 18 GHz.
Interestingly, one connector company is solely dedicated to providing products that are no longer available. The Aviel Electronics division (Las Vegas, NV) of RF Industries can fabricate functional equivalents for most RF coaxial connectors and adapters that are obsolete, discontinued, or no longer available. The connectors are available in all common interfaces including SMA, SMB, SMC, MCX, and larger interfaces like BNC, TNC, N, C, SC, HN, LT, and LC. Typical body materials and contacts materials are used. Body configurations include straight, right angle, bulkhead, flange mount, blind-mate, tri-axial, and others.
Connector products are part of the long history of Winchester Electronics (Wallingford, CT). Among its newer products is the QC-SMA series, which incorporates a push/pull style of mating that does not require special tooling for mating/unmating. When mated, these connectors can rotate 360 deg. The QC-SMA plugs are fully intermateable with any standard SMA jacks or Winchester's SMA bulkhead jacks. The connectors' electrical performance is comparable to a standard SMA up to 6 GHz. Designs are available for both flexible and semi-rigid-type cables.
Quite a few newer product lines hail from Delta Electronics Manufacturing Corp. (Beverly, MA). The Delta MC-Card connectors can serve as an alternative to MMCX connectors in many wireless and telecom applications. These microminiature, 50-Ω impedance connectors offer snap-on coupling and a frequency range of DC to 6 GHz. They are best suited for use with cables in the range of 0.070 to 0.120 in. diameter as well as metric miniature cables. The connectors provide small size and light weight with the convenience of snapon mating and the ability to rotate connector pairs after mating for precise alignment.
Although the connector's design may seem to have been "perfected" by numerous expert companies, new, innovative approaches are always being developed. Andrew Corp. (Westchester, IL) just announced the Weathershield Connector Protection Enclosure family with a reusable weatherproofing system for cable connections. The WeatherShield Connector Protection Enclosures seal and protect the connections between 1/2-in. jumpers and devices, such as diplexers and tower-mounted amplifiers, from the environment. They also protect the in-line connections between 1/2-in. jumpers and 1 5/8-in., 1 1/4-in., and 7/8-in. coaxial-cable feeders. The one-piece weatherproofing enclosure provides a high-temperature-resistant, watertight seal around the connectors. It also helps to dampen vibration, which can loosen connector interfaces over time.
In the telecommunications arena, the SPOX Blind-mate Interface (BMI) connectors from Molex, Inc. (Lisle, IL) recently made news by offering a self-aligning feature in a small blind-mate package. The low-profile design allows for a mated stack distance of 11.00 mm (0.430 in.). A dual-row, panel-mount design on 2.50 mm (0.098 in.) centerline spacing provides rugged support for blind-mating applications and permits up to 3.00 mm (0.120 in.) misalignment between connectors horizontally and verticallyprior to engagement. The headers are molded in LCP high-temperature plastic to meet lead-free-processing requirements. Firstmate/last-break circuits provide sequential engagement of contacts.
These numerous connector examples are just a tiny representation of the actual components that are available and the application areas that drive their development (see sidebar) . The same is true of the cables and cable assemblies that were spotlighted here. Cables and connectors are among the oldest product lines of the RF industry. Yet they remain dynamic. They are continuously being updated to support emerging technologies. As wireless technologies grow, expand, and become ever-more ubiquitous, transmission-line components will continuously evolve to support them. For a more complete listing of the companies that provide cables, connectors, and cable assemblies, please visit the Microwaves & RF Product Data Directory at www.mrf.com.