Electrically tunable microwave filters

• US 5,990,766 A
• Filed: 06/27/1997
• Issued: 11/23/1999
• Est. Priority Date: 06/28/1996
• Status: Expired due to Fees

• Current Assignee: Robert M. Yandrofski, Y. Development, LLC
• Original Assignee: Superconducting Core Technologies, Inc.
• Inventors: Zhang, Zhihang, Weiser, Attila Jr.
• Primary Examiner(s): Ham, Seungsook
• Application Number:
  US08/883,805
• Time in Patent Office: 879 Days
• Field of Search: 333/204, 333/205, 333/219, 333/235, 333/995
• US Class Current: 333/205
• CPC Class Codes: H01P 1/20336 Comb or interdigital filters
• CPC Class Codes: H01P 1/20381 Special shape resonators
• CPC Class Codes: H01P 1/2039 Galvanic coupling between Input/Output
• CPC Class Codes: H01P 7/06 Cavity resonators
• CPC Class Codes: H01P 7/082 Microstripline resonators H01P7/088 takes precedence
• CPC Class Codes: H01P 7/088 Tunable resonators
• CPC Class Codes: H01P 7/10 Dielectric resonators
• CPC Class Codes: Y10S 505/701 Coated or thin film device, i.e. active or passive
• CPC Class Codes: Y10S 505/866 Wave transmission line, network, waveguide, or microwave storage device

Abstract

The tunable filters of the present invention incorporate tunable dielectric materials (e.g., bulk and thin film ferroelectric and paraelectric materials) in contact with segments of resonators that are at an RF voltage maximum to alter the pass band or stop band characteristic of an RF signal outputted by the filter. The biasing circuitry in contact with the tunable dielectric material can include components for inhibiting or retarding the coupling of RF energy to the biasing circuit.

Claims

1. An electrically tunable planar filter, comprising:

an input for an inputted RF signal and an output for an outputted RF signal;

at least one resonator element coupled to the input and output, the at least one resonator element being separated from a ground structure by a dielectric substrate;

a dielectric material having a permittivity that is a function of a voltage applied to the dielectric material; and

a circuit for biasing the dielectric material with the voltage, wherein, in response to the inputted RF signal passing through the resonator element, the resonator element has a distribution of RF voltages along a segment thereof, the distribution including an RF voltage maximum, wherein the dielectric material is in contact with a portion of the segment having the RF voltage maximum, and wherein the biasing circuit comprises a first electrode connected to the resonator element and a second electrode located in a gap between adjacent portions of the resonator element, whereby altering the permittivity alters a characteristic of the outputted RF signal.

2. The electrically tunable planar filter of claim 1, wherein the second electrode and at least one of the adjacent portions of the resonator define a dielectric capacitance and the dielectric capacitance is no more than 25 pf.

3. The electrically tunable planar filter of claim 1, wherein the dielectric material is located in said gap in contact with said adjacent portions.

4. The electrically tunable planar filter of claim 1, wherein a second segment of the resonator element is substantially parallel to the segment.

5. The electrically tunable planar filter of claim 4, wherein a distance between the segment and the second segment is sufficient to define a capacitance therebetween.

6. The electrically tunable planar filter of claim 4, wherein the segment terminates at a first end and the second segment terminates at a second end, the first and second ends being different from one another and being located substantially adjacent to one another and an RF voltage maximum is located at each of the first and second ends.

7. The electrically tunable planar filter of claim 6, wherein the dielectric material is located between the first and second ends.

8. The electrically tunable planar filter of claim 4, wherein the second electrode is substantially parallel with the segment and second segment.

9. The electrically tunable planar filter of claim 1, wherein the dielectric material is one of a ferroelectric or paraelectric material.

20. The electrically tunable planar filter of claim 1, wherein the second electrode is spaced from at least one of the adjacent portions of the resonator element by a distance ranging from about 3 to about 50 microns.

10. An electrically tunable planar filter, comprising:

an input for an inputted RF signal and an output for an outputted RF signal;

at least one resonator element coupled to the input and output, the resonator element having first and second substantially linear segments that are substantially parallel to one another and define a distributive capacitance therebetween;

a dielectric substrate supporting the resonator element;

a dielectric material having a permittivity that is a function of a voltage applied to the dielectric material, the dielectric material being located between the first and second substantially linear segments; and

means for biasing the dielectric material with the voltage, wherein the biasing means includes an electrode located between the first and second substantially linear segments and spaced apart therefrom, the electrode being substantially parallel with the first and second substantially linear segments, whereby altering the permittivity alters a characteristic of the outputted RF signal.

11. The electrically tunable planar filter of claim 10, wherein, in response to the RF signal passing through the resonator element, the resonator element has a distribution of RF voltages along at least one of the first and second substantially linear segments, the distribution including an RF voltage maximum, and the dielectric material is in contact with a portion of the at least one of the first and second substantially linear segments having the RF voltage maximum.

12. The electrically tunable planar filter of claim 10, wherein the first substantially linear segment terminates at a first end and the second substantially linear segment terminates at a second end, the first and second ends being different from one another and being located substantially adjacent to one another, wherein an RF voltage maximum is located at each of the first and second ends, and wherein the dielectric material is located between the first and second ends.

13. The electrically tunable planar filter of claim 10, wherein the electrode is located at a respective distance from each of the first and second substantially linear segments and each of the respective distances range from about 3 to about 50 microns.

14. The electrically tunable planar filter of claim 10, wherein the biasing means comprises a second electrode contacting the resonator element, the dielectric material being located between the first and second substantially linear segments, to define a dielectric capacitance between the electrode and at least one of the first and second substantially linear segments.

15. The electrically tunable planar filter of claim 10, wherein, when the inputted RF signal is passed through the resonator element, the inputted RF signal has a direction of flow and wherein the biasing means comprises a substantially linear electrode contacting the resonator element, at least a portion of the electrode adjacent to the resonator element having an orientation that is normal to the direction of flow.

16. The electrically tunable planar filter of claim 10, wherein the biasing means comprises an electrode in contact with the resonator element, the electrode being configured to be an open circuit for the RF signal.

17. The electrically tunable planar filter of claim 10, wherein the dielectric material has a thickness ranging from about 0.01 to about 50 microns.

18. An electrically tunable planar filter, comprising:

an input for an inputted RF signal and an output for an outputted RF signal;

at least one resonator element coupled to the input and output, the resonator element having first and second substantially linear segments that are substantially parallel to one another and define a distributive capacitance therebetween;

a dielectric substrate supporting the resonator element;

a dielectric material having a permittivity that is a function of a voltage applied to the dielectric material, the dielectric material being located between the first and second substantially linear segments;

means for biasing the dielectric material with the voltage, wherein, in response to the inputted RF signal passing through the resonator element, the resonator element has a distribution of RF voltages along at least one of the first and second substantially linear segments, the distribution including an RF voltage maximum, and the dielectric material is in contact with a portion of the at least one of the first and second substantially linear segments having the RF voltage maximum, the biasing means including an electrode located between the first and second substantially linear segments and spaced apart therefrom, the electrode being substantially parallel with the first and second substantially linear segments and in electrical communication with the dielectric material, whereby altering the permittivity by biasing the electrode alters a characteristic of the outputted RF signal.

19. An electrically tunable planar filter, comprising:

an input for an inputted RF signal and an output for an outputted RF signal;

at least one resonator element coupled to the input and output, the at least one resonator element being separated from a ground structure by a dielectric substrate;

a dielectric material having a permittivity that is a function of a voltage applied to the dielectric material; and

means for biasing the dielectric material with the voltage, wherein, in response to the inputted RF signal passing through the resonator element, the resonator element has a distribution of RF voltages along a segment thereof, the distribution including an RF voltage maximum, wherein the dielectric material is in contact with a portion of the segment having the RF voltage maximum, wherein a second segment of the resonator element is substantially parallel to the segment, and wherein the biasing means comprises an electrode located between the segment and the second segment and spaced apart therefrom, the electrode being substantially parallel with the segment and second segment, whereby altering the permittivity alters a characteristic of the outputted RF signal.

21. An electrically tunable planar filter, comprising:

an input for an inputted RF signal;

an output for an outputted RF signal;

at least one resonator element coupled to the input and output;

a dielectric material having a permittivity that is a function of a voltage applied to the dielectric material; and

a biasing circuit having (a) a first electrode connected to the resonator element and (b) a second electrode in electrical communication with the dielectric material and separated from the resonator element by a gap to define a capacitance therebetween, the dielectric material being located in the gap between the second electrode and the resonator element, whereby altering the permittivity of the dielectric material alters a characteristic of the outputted RF signal.

22. The electrically tunable planar filter of claim 21, wherein adjacent portions of the resonator element are spaced apart from one another and the dielectric material and second electrode are located between the spaced apart adjacent portions.

23. The electrically tunable planar filter of claim 22, wherein the resonator element is defined by a discontinuous conductive strip.

24. The electrically tunable planar filter of claim 21, wherein the resonator element has a distribution of RF voltages along a segment thereof, the distribution including an RF voltage maximum, and wherein the dielectric material is in contact with the segment at the location of the RF voltage maximum and the second electrode is located adjacent to the segment at the location of the RF voltage maximum.

25. The electrically tunable planar filter of claim 21, wherein the resonator element has a distribution of RF voltages along a segment thereof, the distribution including an RF voltage minimum, and wherein the first electrode is in contact with the segment at the location of the RF voltage minimum.

26. The electrically tunable planar filter of claim 21, wherein the resonator element has a distribution of RF voltages along a segment thereof, the distribution including an RF voltage maximum, and wherein the dielectric material is in contact with the segment at the location of the RF voltage maximum and the second electrode is adjacent to the segment at the location of the RF voltage maximum.