Microstrip tunable filters tuned by dielectric varactors

• US 6,525,630 B1
• Filed: 11/02/2000
• Issued: 02/25/2003
• Est. Priority Date: 11/04/1999
• Status: Expired due to Term

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Paratek Microwave Incorporated (Blackberry Limited)
• Inventors: Rong, Yu, Sengupta, Louise C., Zhu, Yongfei
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Chang, Joseph
• Application Number:
  US09/704,850
• Time in Patent Office: 845 Days
• Field of Search: 333/205, 333/204, 333/246, 427/126.3
• US Class Current: 333/205
• CPC Class Codes: H01P 1/20336 Comb or interdigital filters

Abstract

An electronic filter includes a substrate, a ground conductor, an input, an output, a first microstrip line positioned on the substrate and electrically coupled to the input and the output, and a first tunable dielectric varactor electrically connected between the microstrip line and the ground conductor. The input preferably includes a second microstrip line positioned on the substrate and including a portion lying parallel to the first microstrip line. The output preferable includes a third microstrip line positioned on the substrate and including a portion lying parallel to the first microstrip line. The first microstrip line includes a first end and a second end, the first end being open circuited and the varactor being connected between the second end and the ground conductor. The filter further includes a bias voltage circuit including a high impedance line, a radial stub extending from the high impedance line, and a patch connected to the high impedance line for connection to a DC source. In a multiple pole embodiment, the filter further includes additional microstrip lines positioned on the filter substrate parallel to the first microstrip line and additional tunable dielectric varactors electrically connected between the additional microstrip lines and the ground conductor.

Claims

1. An electronic filter comprising:

a substrate;

a ground conductor;

an input;

an output;

a first microstrip line positioned on the substrate, and electrically coupled to the input and the output; and

a first tunable dielectric varactor comprising a composite selected from BSTO—

MgO, BSTO—

MgAl₂O₄, BSTO—

CaTiO₃, BSTO—

MgTiO₃, BSTO—

MgSrZrTiO₆, and combinations thereof, said varactor operable at room temperature and electrically connected between the microstrip line and the ground conductor.

2. An electronic filter according to claim 1, wherein:

the input comprises a second microstrip line positioned on the substrate and having a first portion lying parallel to the first microstrip line; and

the output comprises a third microstrip line positioned on the substrate and having a first portion lying parallel to the first microstrip line.

3. An electronic filter according to claim 1, wherein said first microstrip line includes a first end and a second end, the first end of said first microstrip line being open circuited and said varactor being connected between the second end of said first microstrip line and the ground conductor.

4. An electronic filter according to claim 1, further comprising:

a first bias voltage circuit including a strip line, a radial stub extending from said strip line, and a patch connect to an end of said strip line for connection to a DC source.

5. An electronic filter according to claim 4, wherein said strip line has a higher impedance than said first microstrip line.

6. An electronic filter according to claim 1, wherein said first varactor comprises:

a substrate having a low dielectric constant with a planar surface;

a tunable dielectric layer on the planar surface of the substrate, said tunable dielectric layer including a Barium Strontium Titanate composite; and

first and second electrodes on the tunable dielectric layer and positioned to form a gap between said first and second electrodes.

7. An electronic filter according to claim 6, wherein said Barium Strontium Titanate composite consists of a material selected from the group:

BSTO—

MgO, BSTO—

MgAl₂O₄, BSTO—

CaTiO₃, BSTO—

MgTiO₃, BSTO—

MgSrZrTiO₆, and combinations thereof.

8. An electronic filter according to claim 6, wherein each of the first and second electrodes consists of a material selected from the group:

gold, copper, silver and aluminum.

9. An electronic filter according to claim 1, further comprising:

a second microstrip line positioned on said substrate parallel to the first microstrip line;

a second tunable dielectric varactor electrically connected between the second microstrip line and the ground conductor;

a third microstrip line positioned on said substrate parallel to the first microstrip line;

a third tunable dielectric varactor electrically connected between the second microstrip line and the ground conductor.

10. An electronic filter according to claim 9, wherein the first, second and third microstrip lines are of equal length.

11. An electronic filter according to claim 9, further comprising:

a plurality of bias voltage circuits for supplying bias voltage to said first, second and third varactors, each of said bias voltage circuits including strip line, a radial stub extending from said strip line, and a patch connected to an end of said strip line for connection to a DC source.

12. An electronic filter according to claim 11, wherein said strip line has a higher impedance than said first microstrip line.

13. An electronic filter according to claim 9, wherein each of said second and third microstrip lines includes a first end and a second end, the first end of each of said second and third microstrip lines being open circuited, said second tunable varactor being connected between the second end of said second microstrip line and the ground conductor, and said third tunable varactor being connected between the second end of said third microstrip line and the ground conductor.

14. An electronic filter according to claim 9, wherein each of said varactors comprises:

a substrate having a low dielectric constant with a planar surface;

a tunable dielectric layer on the planar surface of the substrate, said tunable dielectric layer including a Barium Strontium Titanate composite; and

first and second electrodes on the tunable dielectric layer and positioned to form a gap between said first and second electrodes.

15. An electronic filter according to claim 14, wherein said Barium Strontium Titanate composite consists of a material selected from the group:

BSTO—

MgO, BSTO—

MgAl₂O₄, BSTO—

CaTiO₃, BSTO—

MgTiO₃, BSTO—

MgSrZrTiO₆, and combinations thereof.

16. An electronic filter according to claim 14, wherein each of the first and second electrodes consists of a material selected from the group:

gold, copper, silver and aluminum.