Low-loss tunable radio frequency filter
View Patent ↗A tunable radio frequency (RF) filter is provided. The RF filter comprises 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, and a plurality of non-resonant elements coupling the resonant elements together. The resonant elements are coupled 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. 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 sub-bands(s). The variable non-resonant element(s) may be configured for displacing the reflection zero(es) along the stop band to selectively move the pass band within the one sub-band or within selected ones of the sub-bands.
1. A radio frequency (RF) filter, comprising:
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; and
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.
2. The RF filter of claim 1 , wherein the at least one sub-band comprises a plurality of sub-bands.
3. The RF filter of claim 2 , 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.
4. The RF filter of claim 3 , wherein the pass band has substantially different bandwidths within the selected sub-bands.
5. The RF filter of claim 2 , 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.
6. The RF filter 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.
7. The RF filter of claim 1 , wherein the at least one reflection zero comprises a plurality of reflection zeroes.
8. The RF filter of claim 1 , wherein the at least one variable non-resonant element comprises a plurality of variable non-resonant elements.
9. The RF filter of claim 1 , further comprising at least one tuning element configured for modifying the frequency of at least one of the resonant elements.
10. The RF filter of claim 9 , wherein the at least one tuning element is configured for modifying the frequency of the at least one resonant element to displace the transmission zero corresponding to each frequency of the at least one resonant element along the stop band relative to the at least one reflection zero.
11. The RF filter of claim 9 , wherein the at least one tuning element comprises a plurality of tuning elements configured for modifying the frequencies of the resonant elements to simultaneously displace the stop band with the pass band along a frequency range.
12. The RF filter of claim 1 , wherein the at least one variable non-resonant element has an adjustable susceptance.
13. The RF filter 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.
14. The RF filter of claim 1 , wherein each of the resonant elements comprises a thin-film lumped element structure.
15. The RF filter of claim 14 , wherein the thin-film lumped element structure comprises a high temperature superconductor (HTS).
16. The RF filter of claim 1 , further comprising a controller configured for generating electrical signals to adjust the at least one variable non-resonant element.
17. A radio frequency (RF) filter, comprising:
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; and
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 plurality of sub-bands between the transmission zeroes; and
an electrical controller configured for varying at least one of the non-resonant elements to introduce at least one reflection zero along the stop band to create a pass band within selected ones of the sub-bands.
18. The RF filter of claim 17 , wherein the pass band has substantially different bandwidths within the selected sub-bands.
19. The RF filter of claim 17 , wherein the electrical controller is configured for varying the at least one non-resonant element to displace the at least one reflection zero along the stop band to create another pass band within another one of the sub-bands.
20. The RF filter of claim 17 , wherein the electrical controller is configured for varying the at least one non-resonant element to displace the at least one reflection zero along the stop band to selectively move the pass band within each of the selected sub-bands.
21. The RF filter of claim 17 , wherein the at least one reflection zero comprises a plurality of reflection zeroes.
22. The RF filter of claim 17 , wherein the at least one non-resonant element comprises at least two non-resonant element.
23. The RF filter of claim 17 , further comprising a plurality of tuning elements configured for modifying the frequencies of the resonant elements to independently displace the respective transmission zeroes relative to the at least one reflection zero.
24. The RF filter of claim 17 , wherein the electrical controller is configured for adjusting a susceptance of the at least one non-resonant element.
25. The RF filter of claim 17 , wherein the at least one non-resonant element comprises at least one of a variable capacitor, loss-loss switch, a varactor, and a switched capacitor.
26. The RF filter of claim 17 , wherein each of the resonant elements comprises a thin-film lumped element structure.
27. The RF filter of claim 17 , further comprising a controller configured for generating electrical signals to adjust the at least one variable non-resonant element.
28. The RF filter of claim 17 , wherein the thin-film lumped element structure comprises a high temperature superconductor (HTS).
29. A radio frequency (RF) filter, comprising:
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; and
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 have susceptance values that locate at least one reflection zero within the stop band to create a pass band in one of the at least one sub-bands.
30. The RF filter of claim 29 , wherein the at least one sub-band comprises a plurality of sub-bands.
31. The RF filter of claim 29 , wherein the at least one reflection zero comprises a plurality of reflection zeroes.
32. The RF filter of claim 29 , wherein each of the resonant elements comprises a thin-film lumped element structure.
33. The RF filter of claim 32 , wherein the thin-film lumped element structure comprises a high temperature superconductor (HTS).
34. A radio frequency (RF) filter, comprising:
a signal transmission path having an input and an output;
a plurality of nodes disposed along the signal transmission path;
a plurality of resonant branches respectively extending from the nodes;
a plurality of non-resonant branches respectively extending from the nodes;
a plurality of resonant elements respectively coupled to the resonant branches;
a plurality of non-resonant elements, some of which are respectively coupled to the non-resonant branches;
a plurality of transmission zeroes corresponding to resonant frequencies of the resonant elements; and
at least one reflection zero formed between the transmission zeroes to create a pass band.
35. The RF filter of claim 34 , wherein the non-resonant elements comprise at least one variable non-resonant element for selectively displacing the at least one reflection zero relative to the transmission zeroes.
36. The RF filter of claim 34 , wherein plurality of transmission zeroes comprises more than two transmission zeroes.
37. The RF filter of claim 34 , wherein the at least one reflection zero comprises a plurality of reflection zeroes.
38. The RF filter of claim 34 , wherein each of the resonant elements comprises a thin-film lumped element structure.
39. The RF filter of claim 38 , wherein the thin-film lumped element structure comprises a high temperature superconductor (HTS).
40. A method of tuning a radio frequency (RF) filter having a stop band that defines a tuning range, the method comprising:
modifying the RF filter from a first frequency configuration to a second frequency configuration, wherein the RF filter, when in the first frequency configuration, has a first set of pass band characteristics within the tuning range defined by the stop band, and wherein the RF filter, when in the second frequency configuration, has a second different set of pass band characteristics within the tuning range of the stop band.
41. The method of claim 40 , wherein the first and second pass band characteristics have different center frequencies.
42. The method of claim 40 , wherein the first and second pass band characteristics have different bandwidths.
43. The method of claim 40 , wherein the first and second pass band characteristics have different numbers of non-contiguous pass bands.
44. The method of claim 40 , wherein the RF filter is modified from the first frequency configuration to the second frequency configuration by displacing at least one reflection zero within the stop band.
45. The method of claim 44 , wherein the stop band has a plurality of transmission zeroes, and wherein the at least one reference zero is displaced in frequency more than the transmission zeroes are displaced in frequency.
46. The method of claim 40 , wherein the insertion loss of the RF filter is minimized when modifying the RF filter from the first frequency configuration to the second frequency configuration.