What Is an Ultra High Frequency Cable?
A ultra high frequency cable is a cable used for connection between devices that use high frequencies.
Normally, the inner conductor is surrounded by an insulator, and the outer conductor is concentrically arranged around the insulator. In addition, it is covered with a sheath.
Uses of Ultra High Frequency Cables
Ultra high frequency cables are used to connect devices that use high frequencies. As such, they are often used between TV and Internet transmitting devices that emit radio waves in the high frequency band and their modules. Another application is the connection between the main body and the power supply of devices such as microwave ovens and plasma generators.
Plasma reactions are often used in the field of precision engineering, such as in the field of semiconductors. Together with plasma generators, ultra high frequency cables are an indispensable part of modern society.
Principle of Ultra High Frequency Cables
Ultra high frequency cables consist of a copper wire, called the inner conductor, running through the center, an insulator surrounding the inner conductor, and an outer conductor arranged in concentric circles surrounding the insulator. In addition, it is covered with a sheath. In other words, high-frequency signals are transmitted by the inner conductor.
The transmission efficiency of high-frequency signals is determined by the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor and the dielectric constant of the insulator inserted between the conductors. Therefore, it must be noted that the characteristics of an ultra high frequency cable are not determined by its external appearance, but by its internal structure.
In addition, ultra high frequency cables must transmit high frequency signals stably and efficiently from the generating power source to each module, and must also minimize the effects of external noise. In this noise countermeasure, the outer conductor functions as a shield.
To transmit ultra high frequency signals efficiently, the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor must be maintained concentrically over the entire area of the cable. Bending the cable may cause the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor to collapse. Therefore, a limit bending radius is specified for ultra high frequency cables to ensure that the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor is maintained.
Types of Ultra High Frequency Cables
In general, coaxial cables for ultra high frequency cables are widely used for transmission of ultra high frequency signals. In a typical case where signals received by an antenna are transmitted to a TV or recorder, ultra high frequency cables with a characteristic impedance of 75Ω are the most common type of high frequency cable used.
Ultra high frequency cables are identified by their part numbers, such as “5D-2V” and “S7C-FB” as described below. These numbers and letters indicate the size and material:
1. 5D-2V
- 5: Approximate outer diameter of outer conductor 5mm
- D: Characteristic impedance 50Ω
- 2: Insulator is PE (translucent)
- V: Outer conductor is single conductor braided
2. S-7C-FB
- S: Acronym for Satellite (DIGITAL is also available)
- 7: Approximate outer conductor diameter 7mm
- C: Characteristic impedance 75Ω
- F: Insulator is foamed PE (white)
- B: Braided wire with aluminum foil tape
In ultra high frequency cables, the distance between the inner and outer conductors increases as the cable gets thicker due to its structure. Then, when a certain frequency is exceeded, the characteristic impedance changes, resulting in a phenomenon of increased loss. This frequency is called the limiting frequency and must be lower than this frequency.
The thicker the cable, the lower the limiting frequency. Therefore, semi-rigid cables, in which the outer conductor is a copper tube in a thin cable with a coaxial structure, are used for transmission of ultra high frequency cables exceeding several GHz.
Other Information on Ultra High Frequency Cables
Connectors for Ultra High Frequency Cables
Since various types of connectors are available for ultra high frequency cables, it is important to select the most suitable one for the application. The main factors that determine which type to use are the frequency and power required, as well as impedance, transmission loss, and wiring configuration.
By selecting connectors that match these factors, it is possible to prevent impedance disturbance at the connection point and unwanted reflections due to collapsed braiding of the outer conductor of the coaxial. It is also important to select the most suitable connector, taking into consideration the shape of the connection point and the connection method, such as whether there is a lot of plugging and unplugging.