RF Coaxial Cables are one of the most common types of transmission lines, used in virtually all types of RF applications. From space, aerospace, and defense/military to home television, either 50 Ohm Coaxial Cables or 75 Ohm Coaxial Cables can be found almost everywhere, including test and measurement laboratories, automated test facilities, cellular/wireless telecommunication installations and home entertainment setups. The main advantage of RF coax cables is that they allow for RF interconnection between RF ports that is more efficient and less prone to interference than wireless links. RF cables are also generally lower weight, more compact, and more easily prepared and installed than waveguide interconnects.
An RF coax cable, on the most basic level, is comprised of a conductive inner conductor, dielectric, and outer conductor. However, most coaxial cables have additional outer dielectric jacketing, conductive sheathing/tape, barrier layers, or armor layers to provide enhanced utility for specific applications. The inner conductor of a RFcable is typically copper, or copper coated metal, but may also be made of aluminum or other highly conductive metals. The center conductor is usually solid, but may also be braided to reduce weight and cost. The dielectric spacer is usually a low dielectric constant and low loss dielectric material, such as teflon/PTFE, or similar polymers. The dielectric spacer may be solid, perforated, or even a more complex hollow structure that ensures caoxiality of the inner and outer conductor. The outer conductor of coaxial cables can be a solid, braided, stranded, or even wrapped conductive materials depending on the intended application and performance of the coaxial cable.
Flexible Coax Cables
The most common type of cable is likely the flexible coaxial cable with a thick dielectric outer jacket that helps to ensure coaxiality of the outer conductor, inner conductor, and dielectric spacer during flexure or pulling when installing long runs of coaxial cable. Rigid coaxial cable, while less common, are generally made of solid outer and inner conductors that must be precisely fabricated for an intended application, which makes this coaxial cable type more specialized and often only used in custom installations.
Corrugated Coax Cables
Corrugated coaxial cable are similar to both flexible and rigid coaxial cable, in that the inner and outer conductors are made of solid conductive material, however, the corrugation feature allows for minor flexibility. As long as the corrugations are substantially smaller than a wavelength of the intended signals, then the corrugation feature has minimal impact on the RF performance of the transmission line, which is often better than a braided, stranded, or wrapped coaxial cable inner/outer conductor.
Formable and Semi-Rigid Coax Cables
Formable coaxial cable and semi-rigid coaxial cable are also somewhat similar. Semi-rigid coaxial cables are made in such a way that with the right tools and technique, this type of coaxial cable can be formed to a specific shape, once. The construction of semi-rigid coaxial cable is similar to rigid coaxial cable with the exception that the inner conductor, outer conductor, and dielectric are designed to allow for forming, but only a single occurrence. Hence, semi-rigid coaxial cable offers higher performance than braided, stranded, or wrapped coaxial cable at the cost of greater specialization. Formable coaxial cable are made in such a way that the inner and outer conductors are solid-like conductors, such as tin-filled copper braiding, so perform more similarly to a solid conductor but allow for some flexibility.