Semi-Rigid Cable, Benchmark in RF Performance
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Semi-Rigid Cable

Why use a Semi-Rigid cable? A coaxial cable is considered “semi-rigid” when the outer conductor is formed from a solid seamless metal tube with a diameter generally less than 0.5 inch. The majority of Semi-Rigid cables have an outer diameter between 0.034 and 0.250 inch. Semi-Rigid cables are available off the shelf to fit almost any application requiring the near perfect transmission of RF/microwave energy. Semi-Rigid coaxial cable finds applications from very low frequencies through 110 GHz. Almost any system operating above 500 MHz and in need of good operational performance and total...

How to Select a Semi-Rigid Cable Coaxial cable attenuation is primarily dependent on the materials and size. Cable construction can contribute negatively, for example, stranded center conductors and braided outer shields have considerably more loss than a solid center and outer conductor. The Center Conductor The center conductor is either a solid or stranded metal wire which acts as the primary electrical signal carrier for any coaxial cable. Most attenuation occurs at the surface of the center conductor due to the "skin effect" of microwave signals, making the finish or plating a very...

The Dielectric The insulating material between the center and outer conductor maintains the spacing and geometry of the cable and ensures mechanical integrity during forming and bending. A significant portion of the transmission losses are caused either directly or indirectly by the dielectric. Cables with a low dielectric constant, while offering lower bulk dielectric losses, also require a larger center conductor diameter to maintain the same characteristic impedance. The larger center conductor can substantially lower the overall cable attenuation. In addition, the dielectric determines...

The Outer Conductor Plating The Outer Conductor The outer conductor serves many purposes. It is the electrical shield which contributes to cable attenuation and controls RF leakage. Through precision mechanical tolerances, the outer conductor minimizes return loss (VSWR) by maintaining a constant characteristic impedance. The outer conductor is the primary strength member that keeps connectors firmly attached to the cable. It provides environmental protection and determines the flexibility or how easy the cable can be formed or bent. The most commonly used materials are copper and aluminum...

Plating and Finishes Copper and aluminum conductors are often plated for additional corrosion protection and solderability. The most common plating materials are tin and silver. Both materials are very soft and ductile. Silver has superior electrical conductive properties along with being very corrosive resistant to atmospheric oxygen, although vulnerable to tarnish by atmospheric sulfides and nitrates. Silver plating is the preferred plating anytime the material is part the conductive path inside the cable. For Semi-Rigid cables, silver plating the outer conductor is not recommended for...

White Paper How Does Semi-Rigid cable Deliver Maximum Power Transfer? Why is Semi-Rigid cable Better for Precision Phase Matching? In a coaxial cable, the characteristic impedance is the result of the center (d) and dielectric (D) diameters along with the dielectric constant (e) of the insulator as expressed in the following the equation: Many applications require cable assemblies to be an exact electrical or phase length. Phase matching cable assemblies is typically accomplished by manufacturing the cable assembly slightly longer than required, measuring the electrical length, and then...

What is MIL-DTL-17? No discussion on Semi-Rigid cable is complete without mentioning MIL-DTL-17, the governing military specification for RF cables. MIL-DTL-17 lists five Semi-Rigid cables sizes ranging from 0.034 to 0.250 inch diameter. Within each size group, there are multiple part numbers covering different center and outer conductor materials along with tin, silver, and solder plating. Semi-Rigid cables purchased from the MIL-DTL-17 Qualified Products List (QPL) are guaranteed to meet certain minimal performance requirements aimed at the typical military applications regardless of the...

Why Carlisle Interconnect Technologies? Why Specify a Carlisle Interconnect TechnologiesManufactured Semi-Rigid cable? In 1936, Precision Seamless Tube Company received an inquiry involving an insulated wire in which the customer wanted to be encased in a solid metal tubular sheath for mechanical protection. A sample was produced which worked well for the application, and an order was received. Thinking that the design might be unique, the company applied for, and, in due course, received a patent. The product was called “Metal Shielded Wire”. In 1940, the two partners that owned Precision...

With the largest selection of Semi-Rigid coaxial cables in the industry, CarlisleIT has a solution for almost any transmission line problem. Our extensive line of Semi-Rigid coaxial cables include: Aluminum 50 Ohm Cables Available in both standard and low loss versions, aluminum jacketed cables offer easier bending and significant weight reduction. MIL-DTL-17 Qualified Cables A full range of MIL-DTL-17 qualified cables. These cables undergo additional testing to ensure they are fully capable of satisfying the most demanding military applications. Stainless Steel 50 Ohm Cables Stainless...

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