How to Specify and Select RF Filters

RF filters are critical components in aerospace and defense electronic systems. In high-frequency transmissions, they channel desired signals and reject unwanted signals, enabling reliable signal processing across the RF, microwave, and millimeter wave (mmWave) electromagnetic spectrum. In operating environments with many such signals, including from jammers trying to disrupt the operation of some systems, RF filters are employed in progressively higher frequencies. At the same time, systems engineers are requesting smaller filters that fit within drop-in surface mount technology (SMT) packages mounted within compact printed circuit board (PCB) assemblies.

Selecting a filter for an A&D application requires an understanding of available RF filter responses, physical formats, and technologies, with a good idea of necessary functional goals, such as separating channels or rejecting interference. The optimum filter for an aerospace and defense (A&D) system need not take up much space but should meet or exceed certain performance goals, such as passband insertion loss and stopband rejection. Commercial off-the-shelf (COTS) filters can sometimes provide the performance needed by A&D systems, but custom designs are often needed for top performance. Working closely with a filter designer and manufacturer can meet an A&D system's RF filter requirements in a timely and reliable manner.