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An Introduction To Ceramic Filters
November 14, 2006
Ceramic filters can be either of coaxial form or dielectrically loaded waveguide. Ceramic filters as discussed here are transverse electromagnetic (TEM) coaxial structures using quarter-wave resonators and either capacitive or magnetic coupling. The quarter-wave resonator is formed from a block (usually square) of ceramic material with a hole in the middle parallel to its length. The outside, one end, and the hole are coated with a conductive material (usually silver) to form a shorted quarter wavelength of transmission line. The length vs. frequency of the line is determined by the dielectric constant of the ceramic.
Essentially, ceramic filters are a form of distributed filters. They are much more rugged than LC filters, which are susceptible to vibration and microphonics. Ceramic filters are much less expensive to produce than either LC or cavity-type filters, due to the reduced labor, material, and machining costs. In addition, most modern ceramic materials are extremely temperature stable with temperature coefficients of < 5 ppm. Typically, ceramic filters are much less temperature sensitive than either LC or cavity filters, even after compensation.
This article will cover the basics of ceramic filters by answering some of the most commonly asked questions about these components.
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