Dual bandstop filter with enhanced upper passband response
View Patent ↗A dual bandstop filter affects frequencies in a lower passband, first and second stopbands separated by a middle passband, and an upper passband. The filter includes two legs. In one version, one leg is a highpass filter while the other leg is a bandstop filter outputting into a lowpass filter. In a second version, one leg is a lowpass filter while the other leg is highpass filter outputting into a bandstop filter. The first version is preferred when the upper value of the lower passband is around 100 MHz or less, while the second version is preferred when the upper value of the lower passband is around 100 MHz or more. In a third version, one leg is a highpass filter while the other leg is a bandstop filter sandwiched between two lowpass filters, preventing second resonances from the lowpass filter from interfering with desired frequencies in the upper passband.
1. A dual bandstop filter which affects frequencies in a lower passband, first and second stopbands separated by a middle passband, and an upper passband, comprising:
first and second legs connected in parallel;
when an upper value of the lower passband is about 100 MHz or less, the first leg is a first highpass filter while the second leg is a first bandstop filter outputting into a first lowpass filter; and
when the upper value of the lower passband is about 100 MHz or more, the first leg is a second lowpass filter while the second leg is a second highpass filter outputting into a second bandstop filter.
2. A dual bandstop filter according to claim 1 , wherein all circuit components consist of capacitors and inductors.
3. A method of making a dual bandstop filter which affects frequencies in a lower passband, first and second stopbands separated by a middle passband, and an upper passband, comprising the steps of:
providing first and second circuit legs;
connecting the first and second legs in parallel;
making the first leg a highpass filter when an upper value of the lower passband is about 100 MHz or less, and making the second leg a first bandstop filter outputting into a first lowpass filter; and
making the first leg a second lowpass filter when the upper value of the lower passband is about 100 MHz or more, and making the second leg a second highpass filter outputting into a second bandstop filter.
4. A method according to claim 3 , comprising the further step of making all circuit components of capacitors and inductors.