Low-loss tunable radio frequency filter
View Patent ↗A method of constructing an RF filter comprises designing an RF filter that includes a plurality of resonant elements disposed, a plurality of non-resonant elements coupling the resonant elements together to form a stop band having a plurality of transmission zeroes corresponding to respective frequencies of the resonant elements, and a sub-band between the transmission zeroes. The non-resonant elements comprise a variable non-resonant element for selectively introducing a reflection zero within the stop band to create a pass band in the sub-band. The method further comprises changing the order in which the resonant elements are disposed along the signal transmission path to create a plurality of filter solutions, computing a performance parameter for each of the filter solutions, comparing the performance parameters to each other, selecting one of the filter solutions based on the comparison of the computed performance parameters, and constructing the RF filter using the selected filter solution.
1. A method of constructing a radio frequency (RF) filter, comprising:
designing a radio frequency (RF) filter that includes a signal transmission path having an input and an output, a plurality of resonant elements disposed along the signal transmission path between the input and the output, a plurality of non-resonant elements coupling the resonant elements together to form a stop band having a plurality of transmission zeroes corresponding to respective frequencies of the resonant elements, and at least one sub-band between the transmission zeroes, wherein the non-resonant elements comprise at least one variable non-resonant element for selectively introducing at least one reflection zero within the stop band to create a pass band in one of the at least one sub-bands;
changing the order in which the resonant elements are disposed along the signal transmission path to create a plurality of filter solutions;
computing a performance parameter for each of the filter solutions;
comparing the performance parameters to each other;
selecting one of the filter solutions based on the comparison of the computed performance parameters; and
constructing the RF filter using the selected filter solution.
2. The method of claim 1 , further comprising generating a coupling matrix representation for each of the filter solutions, wherein the performance parameter for each of the filter solutions is computed from the respective coupling matrix representation.
3. The method of claim 2 , wherein the filter design includes nodes respectively between the first set of non-resonant elements, nodes respectively between the plurality of resonant elements and the second set of non-resonant elements, and nodes at the input and output, wherein each dimension of the coupling matrix includes the nodes.
4. The method of claim 3 , further comprising reducing each coupling matrix to its simplest form, and determining whether the reduced coupling matrices are different relative to each other.
5. The method of claim 1 , wherein the performance parameter is one or more of an intermodulation distortion, insertion loss, and power handling.
6. The method of claim 1 , wherein the at least one sub-band comprises a plurality of sub-bands.
7. The method of claim 6 , wherein the at least one variable non-resonant element is for displacing the at least one reflection zero along the stop band to create the pass band within selected ones of the sub-bands.
8. The method of claim 7 , wherein the pass band has substantially different bandwidths within the selected sub-bands.
9. The method of claim 6 , wherein the at least one variable non-resonant element is for displacing at least another reflection zero within the stop band to create another pass band within another one of the sub-bands.
10. The method of claim 1 , wherein the at least one variable non-resonant element is for displacing the at least one reflection zero along the stop band to selectively move the pass band within the one sub-band.
11. The method of claim 1 , wherein the at least one reflection zero comprises a plurality of reflection zeroes.
12. The method of claim 1 , wherein the at least one variable non-resonant element comprises a plurality of variable non-resonant elements.
13. The method of claim 1 , wherein the RF filter has at least one tuning element configured for modifying the frequency of at least one of the resonant elements.
14. The method of claim 1 , wherein the at least one variable non-resonant element has an adjustable susceptance.
15. The method of claim 1 , wherein the at least one variable non-resonant element comprises at least one of a variable capacitor, a loss-loss switch, a varactor, and a switched capacitor.
16. The method of claim 1 , wherein each of the resonant elements comprises a thin-film lumped element structure.
17. The method of claim 16 , wherein the thin-film lumped element structure comprises a high temperature superconductor (HTS).
18. The method of claim 1 , wherein each of the resonant elements is an acoustic resonator.
19. The method of claim 1 , wherein the RF filter further includes a controller configured for generating electrical signals to adjust the at least one variable non-resonant element.
20. The method of claim 1 , wherein the number of the plurality of resonant elements is at least four.
21. A method of constructing a radio frequency (RF) filter, comprising:
designing a radio frequency (RF) filter that includes a signal transmission path having an input and an output, a plurality of resonant elements disposed along the signal transmission path between the input and the output, a plurality of non-resonant elements coupling the resonant elements together to form a stop band having a plurality of transmission zeroes corresponding to respective frequencies of the resonant elements, and at least one sub-band between the transmission zeroes, wherein the non-resonant elements comprise at least one non-resonant element that introduces at least one reflection zero within the stop band to create a pass band in one of the at least one sub-bands;
changing the order in which the resonant elements are disposed along the signal transmission path to create a plurality of filter solutions;
computing a performance parameter for each of the filter solutions;
comparing the performance parameters to each other;
selecting one of the filter solutions based on the comparison of the computed performance parameters; and
constructing the RF filter using the selected filter solution.
22. The method of claim 21 , further comprising generating a coupling matrix representation for each of the filter solutions, wherein the performance parameter for each of the filter solutions is computed from the respective coupling matrix representation.
23. The method of claim 22 , wherein the filter design includes nodes respectively between the first set of non-resonant elements, nodes respectively between the plurality of resonant elements and the second set of non-resonant elements, and nodes at the input and output, wherein each dimension of the coupling matrix includes the nodes.
24. The method of claim 23 , further comprising reducing each coupling matrix to its simplest form, and determining whether the reduced coupling matrices are different relative to each other.
25. The method of claim 24 , wherein the performance parameter is one or more of an intermodulation distortion, insertion loss, and power handling.
26. The method of claim 22 , wherein the at least one sub-band comprises a plurality of sub-bands.
27. The method of claim 22 , wherein the at least one reflection zero comprises a plurality of reflection zeroes.
28. The method of claim 22 , wherein the at least one non-resonant element comprises a plurality of non-resonant elements.
29. The method of claim 22 , wherein the RF filter has at least one tuning element configured for modifying the frequency of at least one of the resonant elements.
30. The method of claim 22 , wherein the number of the plurality of resonant elements is at least four.