Feed through capacitors are originally designed for DC power line in RF module or system. It passed through the DC (and low frequency signals) but blocks the RF energy. In practical use the: feed through capacitors are fitted to the metal case of the RF module on holes where the wires enter the system. They let the signal pass through but will stop the RF from escaping from the device through that hole to the outside wiring.
A feed-through capacitor in which a composite dielectric layer made of a mixed material containing a resin material and dielectric material powder is arranged between a feedthrough terminal and an outer electrode terminal surrounding this feedthrough terminal, a capacitance being formed between the
feed through terminal and the outer electrode terminal.
A ceramic plate is formed with sleeve-like protuberances with an internal aperture, the plate is metalized around the sleeve-like protuberances, and feed-through conductors are placed through the apertures, the metallized coating around the protuberances and the feedthrough conductor forming the capacitance; the metalized coating is removed from the zones surrounding the terminal ends of the openings, to provide ceramic insulation material between the feed-through conductors and the metalized coating. The metalized coating may be removed by grinding.