Narrow band-pass filter with primary and secondary sets of resonators having out-of-band resonant frequencies that are different from each other
View Patent ↗A narrowband filter tuned at a center frequency. The filter comprises an input terminal, an output terminal, and a plurality of resonators coupled in cascade between the input terminal and the output terminal. Each of the resonators is tuned at a resonant frequency substantially equal to the center frequency. The resonant frequencies of a primary set of the resonators and a secondary set of the resonators are of different orders.
1. A narrowband filter having a desired pass band, comprising:
an input terminal;
an output terminal; and
a plurality of resonators coupled in cascade between the input terminal and the output terminal, the plurality of resonators are grouped into a primary set of the plurality of resonators and a secondary set of the plurality of resonators, the primary set of resonators having an in-band resonant frequency and at least one out-of-band resonant frequency, wherein the secondary set of resonators have a plurality of resonant frequencies, all of which are different from the at least one out-of-band resonant frequency of the primary set of resonators, such that the at least one out-of-band resonant frequency of the primary set of resonators is suppressed.
2. The narrowband filter of claim 1 , wherein the plurality of resonators are coupled between the input terminal and the output terminal in a manner that characterizes the filter as a band-pass filter.
3. The narrowband filter of claim 1 , wherein each of the secondary set of resonators has an in-band resonant frequency that is of a different order than the in-band resonant frequency of the primary set of resonators, wherein the in-band resonant frequency of the primary set of resonators and the each in-band resonant frequency of the secondary set of resonators are substantially equal to a center frequency of the desired pass band of the narrowband filter.
4. The narrowband filter of claim 3 , wherein the in-band resonant frequency of the primary set of resonators is a second order, and the in-band resonant frequency of each of the secondary set of resonators is a first order.
5. The narrowband filter of claim 1 , wherein the at least one out-of-band resonant frequency of the primary set of resonators comprises a plurality of out-of-band resonant frequencies.
6. The narrowband filter of claim 1 , wherein the primary set of resonators comprises at least two resonators.
7. The narrowband filter of claim 6 , wherein the secondary set of resonators is coupled between the at least two resonators.
8. The narrowband filter of claim 7 , wherein the secondary set of resonators comprises at least two resonators.
9. The narrowband filter of claim 1 , wherein each of the plurality of resonators comprises a planar structure.
10. The narrowband filter of claim 1 , wherein each of the plurality of resonators comprises a microstrip structure.
11. The narrowband filter of claim 1 , wherein each of the plurality of resonators comprises a transmission line composed of high temperature superconductor (HTS) material.
12. The narrowband filter of claim 1 , wherein a center frequency of the pass band is in the microwave range.
13. The narrowband filter of claim 12 , wherein the center frequency is in the range of 800-900 MHz.