What Is an RF Filter?
A filter is an element or circuit that discriminates frequencies, allowing only signals in the required frequency band to pass through and blocking other signals.
An RF filter is a filter for broadcasting wireless communication signals using radio frequency (RF).
In the case of digital terrestrial broadcasting, signals in the 80 to 800 MHz frequency band are used. For cell phones such as smartphones, signals in the 800-3500 MHz frequency band are used. Therefore, an RF filter is used to block signals outside of these frequency bands when they are mixed in.
Uses of RF Filters
The frequencies used for broadcasting and communications are regarded as a finite national asset, and the frequency bands used for each service are determined to use them effectively.
It is necessary to take measures to prevent interference between the two services from adversely affecting each other’s services. RF filters are effective for this purpose.
For example, RF filters are used to receive digital terrestrial broadcasts, allowing only the 80 to 800 MHz broadcast signals to pass through and blocking signals outside this range.
RF filters are available in a compact size and are as thick as an antenna cable, and are used by connecting them vertically to the antenna cable.
Principles of RF Filters
As mentioned above, RF filters are used for TV reception, cellular phones, and other industrial equipment.
Television broadcasting frequencies range from 80 to 800 MHz, while cellular phone communication frequencies are on the upper end of that range, from 800 to 3500 MHz. The frequency bands used by the two are separated, so problems should not occur.
However, if the frequencies handled by the internal circuits of the cellular phone step into the frequency band of the TV due to some trouble or equipment design problem, for example, there is a possibility that the image and sound on the TV side may be affected as noise.
In such a case, RF filters that allow only the signals in the frequency band of the TV set to pass through can be inserted in the TV set to prevent the problem.
Although this level of support may not be necessary when watching TV in the home, it is a possible safety measure to avoid problems due to noise contamination during the viewing process when using TVs for business purposes.
Industrial equipment requires more precise operation than consumer equipment, and it is necessary to eliminate as much as possible the reception of unnecessary radio waves that could cause malfunctions.
A special example of semiconductor manufacturing equipment, for example, is required to operate at 13.6 MHz, 27.1 MHz, and 40.7 MHz due to the product’s characteristics.
RF filters pass only signals in the frequency range of around 13.6MHz, 27.1MHz, and 40.7MHz.
For this reason, a variety of RF filters are available. Some filters can extract only specific frequency bands, while others can be configured to change the frequency bands that can be removed.