A coaxial cable is one that consists of two conductors that share a common axis. The inner conductor is typically a straight wire, either solid or stranded and the outer conductor is typically a shield that might be braided or a foil. Coaxial cable is a cable type used to carry radio signals, video signals, measurement signals and data signals. Coaxial cable exists because we can't run open-wire line near metallic objects (such as ducting) or bury it.
We trade signal loss for convenience and flexibility. Coaxial cable consists of an insulated center conductor which is covered with a shield. The signal is carried between the cable shield and the center conductor. This arrangement give quite good shielding against noise from outside cable, keeps the signal well inside the cable and keeps cable characteristics stable.
Coaxial cables and systems connected to them are not ideal. There is always some signal radiating from coaxial cable. Hence, the outer conductor also functions as a shield to reduce coupling of the signal into adjacent wiring. More shield coverage means less radiation of energy (but it does not necessarily mean less signal attenuation).
Flexible (Braided) Coaxial Cable is by far the most common type of closed transmission line because of its flexibility. It is a coaxial cable, meaning that both the signal and the ground conductors are on the same center axis. The outer conductor is made from fine braided wire, hence the name "braided coaxial cable". This type of cable is used in practically all applications requiring complete shielding of the center conductor.
Semirigid Coaxial Cable uses a solid tubular outer conductor, so that all the RF energy is contained within the cable. For applications using frequencies higher than 30 GHz a miniature semirigid cable is recommended.
Ribbon Coaxial Cable combines the advantages of both ribbon cable and coaxial cable.
Ribbon Coaxial Cable consists of many tiny coaxial cables placed physically on the side of each other to form a flat cable. Each individual coaxial cable consists of the signal conductor, dielectric, a foil shield and a drain wire which is in continuous contact with the foil.
The entire assembly is then covered with an outer insulating jacket. The major advantage of this cable is the speed and ease with which it can be mass terminated with the insulation displacement technique.