To connect devices with the mobile network, a connection between the antennas and the respective receivers is required. This is achieved via the so-called coaxial cables. The connection between the antenna/device and cable takes place at the connection point via a coaxial connector (read this article to discover more detailed information regarding the characteristics and versions of such connectors).
Coaxial cables can transmit high-frequency, broadband signals and are generally low-loss. They are used, for example, for radio signals, radar signals, or even for mobile radio signals. The following article deals with this special use case.
Structure of antenna cables:
Similar to antenna connectors, coaxial cables basically consist of four parts, which together determine the quality of the cable. The core of each antenna cable is the inner conductor, which transports the mobile radio signal. Usually, the material used for this is copper, which is often silver-plated or tin-plated. Inner conductors can be rigid, or there are flexible types, in the form of stranded wires. The core of the cable is surrounded by isolation material, the dielectric. It separates the inner conductor from the outer conductor, being usually made of plastic or also of air.
The outer conductor guarantees an electrical shielding from the external environment and protects the inner conductor from interference signals. A coaxial cable can be single or double shielded.
Each antenna cable has an outer sheath, which represents the last layer. This consists of a plastic layer and does not influence the electrical properties of the cable. However, the sheath is important, as it protects the cable from environmental influences. For example, some of the important features here include the temperature range in which the cable can be used, or also the resistance to chemicals, fire and UV radiation.
Properties of antenna cables:
One of the most important physical features of coaxial cables is the characteristic impedance. This is characteristic for an antenna cable and is determined by the cable cross section. The decisive factor here is the ratio between the diameter of the inner conductor and the inner diameter of the outer conductor. In addition, the properties of the insulation material within the dielectric play a significant role.
The impedance must be constant across various cables and connectors that are used, without being influenced by the frequency. Accordingly, when selecting coaxial cables and connectors, for the connection of antennas and receivers, one must always consider the required characteristic impedance. With mobile communications, this is classically of 50Ω.
The attenuation is also important, as it indicates the signal loss when passing through an inner conductor. This is usually specified in decibels per meter and it depends on the frequency to be transmitted: the higher this is, the higher the attenuation is going to be. In addition, the signal loss is determined by various factors that depend on the antenna cable. This includes first of all the diameter of the inner conductor: thick coaxial cables comparatively lose less signal than thin ones, and are therefore usually preferred. Additional factors include the texture and the material of the conductor. For example, rigid conductors have a lower loss than stranded conductors, and silver-plated copper has a lower attenuation than pure copper. The age of the cable and the temperature to which it is exposed also play a role.
Selecting the right cable version for mobile communications:
Which coaxial cable is the „best“ depends on the individual application scenario. Here, among other things, the above-described properties are decisive: the impedance must be matched between cables and connectors. The attenuation depends on the frequency in which the mobile signal is to be transmitted. When interpreting the manufacturer’s specifications, attention must be paid to this.
The required length is another selection criteria. This depends on the installation location. Basically: the shorter the cable, the lower the attenuation. However, at the same time, a short cable naturally goes hand in hand with a limited choice of locations for the antenna.
In addition, the various coaxial cables differ in thickness: the larger the diameter, the better the shielding from interference signals and the lower the signal loss. However, thicker coaxial cables also have less mechanical flexibility, which can represent a hindrance, depending on the application scenario.
Last but not least, when it comes to the selection of a suitable antenna cable, the price also plays a role. Here, there can be significant differences between the various cable versions and manufacturers.
For LTE applications, common coaxial cables are, for example, the RG-316 U, the KXS-5, or the KXS-7. All of these cables have an impedance of 50Ω, typical for mobile communications.
The RG-316 U coaxial cable has a silver-plated stranded copper as inner conductor. The dielectric is made of PTFE plastic. The cable is simply shielded by an outer conductor, made of silver-plated copper braid. The outer sheath has a diameter of 2,5 mm. Thus, the RG-316 U is very flexible and uncomplicated to use, the minimal bending radius is only 15 mm. However, the flexible inner conductor, the simple shielding and the reduced diameter are also accompanied by a higher attenuation: this is of 0.8 db/m at a frequency of 800 MHz. Given that, the cable is suitable only for short distances to the antenna, of 1-2 meters maximum.
The KXS-5 is also known as the „low loss cable“. A rigid copper wire as inner conductor, a double shielding consisting of a tinned copper braid and an aluminum composite foil, as well as a larger diameter of 4.95 mm ensure here a comparatively low signal loss of 0,32 db/m at 800 MHz. This lower attenuation extends the recommended maximum cable length to 5-10 meters.
For even greater distances of maximum 10-20 meters between antenna and receiver, the KXS-7 is suitable. Here, the inner conductor consists of a stranded copper wire, which is significantly thicker than the inner conductors of the other two cables. The double shielding is composed of a pure copper braid and a copper composite foil. The outer sheath has a diameter of 7.3 mm. As a result, in this comparison, the cable has the lowest attenuation of only 0,21 db/m at 800 MHz.
Are you looking for an antenna which guarantees optimal mobile reception? Feel free to visit our online shop! There you can find a selection of antennas, which provide coverage for LTE, as well as 2G and 3G, and are standardly delivered with a low-loss cable. We are happy to respond to any questions you might have about our products by e-mailor phone at +49 40 35 73 20 65.