How do I design a bandstop filter for rejecting a specific interference signal in a receiver?

A bandstop (notch) filter for rejecting a specific interference signal in a receiver is designed to provide deep rejection (30-60 dB) at the interference frequency while minimally affecting the desired signal on either side of the notch. The design involves: determining the interference frequency and required rejection depth (typically > 30 dB for strong interferers like nearby transmitters, cell towers, or self-generated spurious signals), specifying the notch bandwidth (as narrow as possible to minimize impact on the desired signal; typical notch bandwidth is 0.1-5% of the center frequency), selecting the filter topology (series LC resonator to ground creates a short circuit at resonance, shunting the interference to ground; parallel LC resonator in series with the signal path creates an open circuit at resonance, blocking the interference; coupled-resonator bandstop filter uses multiple resonators for deeper rejection and steeper skirts), and implementing the filter (at low frequencies below approximately 2 GHz, use discrete LC components; at microwave frequencies, use quarter-wave open or shorted stubs, ring resonators, or DGS structures; for very narrow notch bandwidth with high Q, use waveguide cavity or dielectric resonator notch filters). Key design trade-offs: narrower notch bandwidth requires higher-Q resonators (which are physically larger or more expensive), and deeper rejection requires more resonators or higher Q. A single-resonator notch provides 20-35 dB rejection; two cascaded resonators provide 40-60 dB.