Articles
Useful Definitions For Specifying Filters
March 1, 2010
•Application Note: Useful Definitions For Specifying Filters
By Anatech Electronics Inc.
This article defines parameters that are important to understand when specifying Anatech filters and filter-based products. Many of the parameters or specifications described below apply to other Anatech products as well, such as directional couplers, power dividers, and circulators.
TYPES OF FILTERS
Bandpass filter: Passes energy within a certain bandwidth and rejects frequencies below and above this bandwidth.
Bandstop or band-rejection filter: Passes most frequencies without disrupting them but significantly attenuates frequencies over a specific region. A bandstop filter is essentially the opposite of a bandpass filter. A notch filter is a specific type of bandstop filter that has a narrow stopband.
Diplexers and duplexers: These devices are both used to combine two ports into a common port with a high degree of isolation between them so they can employ a single antenna without interfering with each other.
A diplexer is used to combine signals or channels at widely different frequencies and a duplexer can accommodate frequencies or channels that are much closer to each other. Consequently, diplexers are used to combine channels in wireless base station transceivers (for example) and duplexers are used to combine signals in radar or other systems in which the two frequencies are far apart.
Anatech duplexers and diplexers are manufactured from either ceramic, cavity, or SAW filters.
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