RF Coaxial Cables

Today lets discuss a bit of RF coaxial cables. In RF engineering, transmission of signals uses specialize cables to perform the job. These cables are unlike the usual cables that are used in power transmission, such as the ones we see commonly at our home and daily electrical appliances. RF coaxial cables are designed to propagate small signals, which are usually weaker compared to our ACDC currents. And to that end, the design of the cables are done to ensure transmission of signals with minimal losses

Terminations of RF Coaxial

RF cables are made to transmit radio frequency signal. The way to distinguish RF cables can be usually seen from its terminations at both ends, also known as connectors. The connectors are usually separated into two genders (male & female) where opposite gender are required to allow connection.

There are many types of RF cable connectors i.e., BNC, N-type, SMA, SMP, 2.92mm, 2.4mm etc. The key feature of different types of connectors is its ability to operate at different frequency ranges. As a rule of thumb, smaller connectors are more well suited for high frequency operations and vice versa.

Structure of RF Cables

The simple RF coaxial cable structure consist of a central core, an insulator and a metallic shield.

Signal propagation happens at the inner conductor core of the cable. To prevent electromagnetic interference (EMI), a metallic shield is placed to protect the core where the signal is travelling. Obviously, the metallic shield and central core should not come into contact with each other, which is where the dielectric insulator comes into play. The dielectric insulator separates the shield and the signal conductor and prevent each from interfering with the other.

Most coaxial cables will also have a protective outer sleeve or jacket, sometimes even called armor. The jacket adds another layer of protection against outside interference, especially when handled by our hands.

Designing of RF Cables

There are many conditions to be considered when designing a coaxial cable. These parameters are like physical dimension, power handling, flexibility, operating frequency, impedance, rejection performance, and cost. For better flexibility, the outer shield is usually made of a thin foil surrounded by a conductor braid. Typically, the bigger the inner conductor diameter the better the power handling but this will sacrifice the flexibility.

In short, RF cables may look simple outwardly, but as per any RF components, there are many factors to consider in designing them to ensure the best performance. Check out the video below on how a RF coaxial cable can be assembled.