Design Guide: Basic Considerations For Specifying RF And Microwave Filters

As one of the fundamental signal processing components in RF and microwave circuits, the filter plays a critical role in determining any system's ultimate performance. Since the electromagnetic spectrum has become more and more densely populated, filter performance has taken on greater significance than ever because interference rejection is of paramount importance.

To the uninitiated, filters can seem strikingly simple, since they are passive components that perform a single function: to reject RF energy either below or above a specific frequency or range of frequencies or both. However, the truth lies elsewhere, since there are not only multiple types of filters but multiple response types, and descriptions of both are the subject of thousands of technical papers and several textbooks.

Specifying a particular filter for a given system invariably requires a trade-off between a wide variety of factors, including power handling, Q factor, insertion loss, intended operating frequency, size, packaging and mounting, manufacturability, and many other parameters.

Consequently, rather than providing a highly-academic discussion about filter designs and characteristics, this white paper has been created to provide a simple, thumbnail sketch of the most popular filter types (LC, ceramic, cavity, Surface Acoustic Wave (SAW), crystal, and helical) along with the advantages and disadvantages of each in various applications.

Armed with this information, designers can be better equipped to make realistic decisions when specifying a filter and contacting a filter manufacturer, such as Anatech Electronics, Inc.