Low-loss self-switching bandstop filter

A new switchable low-loss bandstop filter is presented based on an indirect switching method combined with all-pass coupled lines. The proposed design allows switching between an all-pass mode and a bandstop filter mode for On/Off operation of a bandstop response. Due to the location of the switch, which is outside of the through line, the passband insertion loss is drastically improved with this new method compared with a conventional switchable bandstop filter configuration. In addition, the method provides consistent group delay throughout the passband in both the all-pass mode and the bandstop filter mode, which is a capability that is not commonly available in conventional multi-path-type switched filter approaches. A 4-pole prototype switchable notch filter centered at 1090 MHz with 14 MHz 30-dB bandwidth was fabricated and measured for demonstration.