What an RF filter does
Filters pass the signals you want and reject the ones you do not. They are essential for suppressing harmonics, protecting receivers from out-of-band interference, and keeping transmitters within emission masks.
Common filter types
- Low-pass — passes signals below a cutoff frequency.
- High-pass — passes signals above a cutoff.
- Band-pass — passes a defined band and rejects everything else.
- Band-stop or notch — removes a narrow interfering band.
Specs that matter
- Insertion loss in the passband.
- Rejection, in dB, at specific stopband frequencies.
- Passband ripple and return loss.
- Power handling and temperature stability.
Choosing a technology
- Ceramic dielectric filters — compact, high Q, ideal for high-volume RF modules. See our ceramic filters.
- Microstrip and stripline — low cost and easy to integrate on a PCB. When the design calls for planar types, look at tunable filters for multi-band coverage.
- Cavity filters — high power and low loss, with a larger footprint.
RFPro tip
Always specify the stopband you need to reject, not just the passband you need to keep. Most filter problems come from under-specified rejection. Browse microstrip filters for your board-level designs, and remember that front-end filtering is often delivered inside integrated RF modules.