AbstractNarrow bandwidth bandstop filters or ‘notch filters’ are frequently required in both communication and electronic warfare systems. In the latter case the ability to switch into an ‘allpass’ state with a minimum level of loss and time delay distortion is vital. Furthermore, in both cases a level of 20‐30 dB rejection is normally required. These factors suggest that the ‘hybrid notch filter’† proposed in this paper is an optimum solution for low‐loss designs. Design techniques and experimental results for two fixed tuned filters for cellular base station applicati