What are Cavity Filters?


If you are looking to find something useful about cavity filters, then you have landed on the right page. This article briefly explains all the important information about cavity filters used in two-way radios. In terms of radio, there are a lot of frequency filters that are used for different purpose. Cavity filter is one of these frequency filters. It is one of the most important factors of modern communication systems. A cavity filter is one of those resonant filters that function to successfully pass the desired RF signals in a defined range of frequency and it can also reject the RF signals in a specific range of frequency. These filters are connected around a Duplexer, and their main function is to let only certain frequencies to pass through them.

Cavity filter uses resonant cavities, and they are constructed from durable materials. They are not made up of those materials that cannot last for more than a couple of years. Some dimensionally stable and highly conductive metals are used in the construction of these cavities. It is because metal is durable, and it can last for many years, even in a severe environment. The cavity filters work as a resonator inside a conducting box. They are constructed in a cylindrical shape along with the axial tuning capacitors.

The wavelength of these cavities is set to ¼ or ¾. Some other cavities are also used in the construction, but they perform less than the resonant cavities, so, they have a shorter wavelength than ¼. The wavelength of the cavities is set due to the combination of width and length of the inner conductor. There is a coupling loop at the output and the input. The length, width, and angle of these loops are also considered to create the wavelength of the cavity. If the loops are located far away from the inner conductor, the “Q” will be high.  It indicates that if the frequency is high, then the “Q” will also be high.

The cavities avoid the interaction of the transmitters in the combining system such as in the weather radios and satellite phones. There is a sideband noise around the channel, and the cavities are used to reduce these voices. The cavities also protect the front end receiver and the automatic gain control circuits. The main principle of the cavity filter is to pass all the desired frequencies through it, and it can also reject the undesired frequencies to pass through it.

The use of cavities in a cavity filter is very necessary. Other tuned circuits can also be used instead of the cavities, but they are not preferred as much as the cavities. It is because the cavities are more effective than the tuned circuits. Moreover, these cavity filters have low insertion loss. It comes with stable temperature options and has high power handling capability.

All in all, cavity filters are known as microwave filters that use cavities to pass and reject the desired and undesired signals at different frequencies in the gigahertz range. The information mentioned above about the cavity filters was all you need to know. I hope this article was helpful for you to gain some knowledge about cavity filters.

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