Wikipedia:Today's featured article/July 17, 2010

A distributed element filter is an electronic filter in which capacitance, inductance and resistance are not localised in discrete capacitors, inductors and resistors as they would be in a conventional filter. Its purpose is to allow a range of signal frequencies to pass, but to block others. Conventional filters are constructed from inductors and capacitors, and the circuits so built are described by the lumped element model, which considers each element to be "lumped together" at one place. That model is conceptually simple, but it becomes increasingly unreliable as the frequency of the signal increases, or as the wavelength decreases. The distributed element model applies at all frequencies, and is used in transmission line theory; many distributed element components are made of short lengths of transmission line. There is no precise frequency above which distributed element filters must be used but they are especially associated with the microwave band. Distributed element filters are used in many of the same applications as lumped element filters, such as selectivity of a radio channel, bandlimiting of noise and multiplexing of many signals into one channel. The technology can be found in several mass-produced consumer items, such as the converters used with satellite television dishes. (more...)

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