Varactor tuning for a narrow band filter
A method and apparatus for providing dynamic and remote tuning of a cryo-cooled bandpass filter is disclosed. The device includes resonator element and a voltage sensitive element as part of the capacitance in a narrow band filter circuit. A varactor such as a GaAs varactor may be used. Alternatively, a capacitor having a voltage-sensitive dielectric such as SrTiO 3 may be used. A computer may be connected to the varactor to provide for automated tuning. The voltage-sensitive capacitor may be integral with the resonator element. The invention provides for remote and dynamic tuning of a narrow bandpass filter while located within its sealed cryo-cooled environment.
1. A tuning device for a cryo-cooled bandpass filter, comprising
a. a resonator element physically located in a cryo-cooled chamber;
b. a voltage-sensitive capacitor operatively connected to the resonator element, wherein when a variable voltage is applied to the voltage-sensitive capacitor, the capacitance of the capacitor is varied, and the resonator frequency changes and shifts the passband characteristics of the filter, the voltage-sensitive capacitor also being physically located in the cryo-cooled chamber, whereby the resonator can be tuned remotely after the cryo-cooled chamber is sealed;
c. a voltage regulator operatively connected to the voltage-sensitive capacitor, wherein the voltage regulator comprises an inductor and a capacitor; and
d. a computer configured and arranged to automatically monitor the output of the filter and to remotely provide real time tuning of the filter.
2. The tuning device of claim 1 , wherein the filter is a narrow band filter.
3. The tuning device of claim 2 , wherein the filter is a ten pole filter.
4. The tuning device of claim 1 , wherein the voltage sensitive capacitor comprises a varactor.
5. The tuning device of claim 4 , wherein the varactor comprises a semiconductor varactor.
6. The tuning device of claim 5 , wherein the varactor comprises a GaAs varactor.
7. The tuning device of claim 1 , wherein the computer is configured and arranged to apply the variable voltage to the voltage-sensitive capacitor.
8. The tuning device of claim 1 , wherein the resonator includes an interdigitalized capacitor and a half loop inductor.
9. The tuning device of claim 8 , wherein said interdigitalized capacitor and said half loop inductor comprise a conductive material on a dielectric substrate.
10. The tuning device of claim 9 , wherein the dielectric substrate is GaAs.
11. A tuning system, comprising:
a. a plurality of the tuning devices of claim 1 ; and
b. a power supply configured to apply the variable voltage alternately to each of the plurality of tuning devices at least once in a predetermined period of time.
12. The tuning system of claim 11 , wherein the capacitor of the voltage regulator of each of the plurality of tuning devices is configured to substantially maintain the variable voltage across the corresponding variable voltage sensitive capacitor for the predetermined period of time after being disconnected from the power supply, whereby the variable voltage applied to the voltage sensitive capacitor of each of the plurality of tuning devices remains substantially unchanged while the power supply applies the variable voltage to the other ones of the plurality of tuning devices.
13. The tuning system of claim 12 , wherein for each tuning device the respective voltage regulator is configured to intermittently apply a voltage to the corresponding capacitor thereof, wherein the capacitance of the corresponding voltage regulator capacitor is sufficient to substantially maintain the voltage across the corresponding voltage regulator capacitor during the time interval between two consecutive applications of the voltage by the respective voltage regulator.
14. The tuning system of claim 13 , wherein the voltage sensitive capacitor comprises a dielectric having a voltage-sensitive dielectric constant.
15. The tuning system of claim 14 , wherein the dielectric comprises a ferroelectric material.
16. The tuning system of claim 15 , wherein the ferroelectric material comprises SrTiO 3 .
17. The tuning system of claim 14 , wherein the voltage sensitive capacitor further comprises a high-temperature superconductor plate, and wherein the resonator element comprises a high-temperature superconductor film comprising the same material as the high-temperature superconductor plate.
18. A tuning device for a bandpass filter, comprising:
a. a resonator comprising
i. a resonator element, and
ii. first and second capacitors, wherein one of the first and second capacitors has a larger capacitance than the other of the first and second capacitors; and
b. a voltage-sensitive device comprising a third capacitor having a voltage sensitive capacitance, wherein the third capacitor is operatively connected in parallel to the second capacitor,
whereby when a variable voltage is applied to the third capacitor, the capacitance of the third capacitor is varied, and the resonator frequency changes and shifts the passband characteristics of the filter.
19. The tuning device of claim 18 , wherein the third capacitor comprises a dielectric having a voltage-sensitive dielectric constant.
20. The tuning device of claim 19 , wherein the dielectric comprises a ferroelectric material.
21. The tuning device of claim 20 , wherein the ferroelectric material comprises SrTiO 3 .
22. The tuning device of claim 19 , wherein the third capacitor further comprises a high-temperature superconductor plate, and wherein the resonator element comprises a high-temperature superconductor film comprising the same material as the high-temperature superconductor plate.
23. The tuning device of claim 18 , wherein the third capacitor comprises a varactor.
24. The tuning device of claim 23 , wherein the varactor comprises a semiconductor varactor.
25. The tuning device of claim 24 , wherein the semiconductor varactor comprises a GaAs varactor.