Radio frequency (RF) cables are a key component in cellular, Global Navigation Satellite Systems (GNSS), Wi-Fi and Bluetooth devices that use external rather than embedded antennas. They carry signals between the antenna and the transmitter and/or receiver, which means they directly affect the performance and reliability of the applications that use those signals.
Coaxial is the most common type of cable. (For information about other types, as well as the relationship between cables and ground planes, see “A Crash Course on RF Cables.”) Coaxial radio frequency (RF) cables have four main components:
- Conductor: Typically made of copper or aluminum, it carries the signal.
- Insulation: Separates the center conductor from shielding and helps signal efficiency. The insulator material typically is a solid or foamed polymer, depending on requirements such as weight and rigidity.
- Shield: Surrounds the insulator, blocking outside interference from nearby electrical and RF sources such as power supplies and transmitters, respectively. The shielding can be a single layer of braided or foil aluminum, or multiple layers of one or both types to maximize protection against interference.
- Jacket: Typically, a thermoplastic material, the jacket protects the shielding, insulator and conductor from physical damage caused by rubbing, pinching, sunlight’s UV rays and even rodents.
All of these materials determine how the cable can be routed in a vehicle or around a building. For example, a thick cable can be challenging to “snake” through a vehicle to the antenna mounted on the roof. But that size and rigidity might not be an issue if the cable is installed on the exterior of a building for a rooftop antenna.
Datasheets Provide Critical Information
The cable’s datasheet is an important resource because it provides information such as weight and minimum bend radius, as well as the temperature range that it’s designed to withstand. The Taoglas antenna builder portal makes it easy to choose a cable type and length and then see its datasheet. For example, here are some specifications for the TGC-200 low-loss cable.
The datasheet also describes the cable’s electrical properties and how the signal’s strength varies by frequency. The following two tables are for the Taoglas TGC-200, which is designed for a wide variety of technologies, such as GNSS, Wi-Fi and sub-6 GHz 4G/5G, where the application requires a cable that maintains low loss even at long lengths of 5-10 meters.
Impedance is one major factor that affects a signal’s strength as it travels down a coaxial cable. Measured in Ohms — such as 50 Ω or 75 Ω — impedance describes the level of electrical resistance that the signal encounters as it travels between the antenna and receiver or transmitter.
50-ohm cables are the most common type of coax for transmitting and transmitting/receiving applications because they do a good job of meeting requirements for both high power handling and low signal loss. 75-ohm cables have lower signal attenuation, which is why they’re generally used for receive-only applications, such as in television and satellite systems.
As the following table shows, the thicker the cable, the lower the signal loss. Thicker cables are more expensive, but their price premium is justifiable if the application involves relatively long cable runs, such as 5-10 meters, and requires low signal loss. This type of cable comparison chart helps OEMs and systems integrators select a cable that strikes the right balance of price, length and signal strength for their particular product, its performance requirements and installation type.
Coaxial cables are another example of why device OEMs and systems integrators should consider antennas early in the design process. Choosing the right type of cable directly affects the performance and reliability of devices and applications. In the case of cellular devices, if the cable is over a certain length, the carrier certification requirements could be relaxed compared to embedded antennas without cables or with short cables.
Taoglas offers a broad selection of off-the-shelf and custom coaxial cable assemblies for cellular, GNSS, Wi-Fi, Bluetooth and other applications. To learn more, visit https://www.taoglas.com/products/cables.
