bandpass filter

The term bandpass filter literally means a device that filters away low and high frequencies, the output consisting of a contiguous range of frequencies allowed to pass through. The common use of the term is for electronic circuits that carry this out on an electronic signal, e.g., within the radio or audio frequency range. Such bandpass filters are used to process radio-telescope signals, and are also common in communications and other radio-based technology.

The wording bandpass filter and its general meaning apply to astronomical filters for visible light and neighboring portions of the EMR spectrum but the phrase is typically used for the above-described electronics. Typical (standardized) optical filters carry out the analogous function, but their technology does not support clean cut-offs of the frequency range. Such spreading of the cut-offs over a frequency range is somewhat true for any bandpass filter, but in the case of UVOIR filters, the term bandpass filter is most often used for specialized narrow-band filters that come closer to a clean cut-off, such as Lyot filters often used for solar telescopes.