Distributed element filter

• US 6,300,849 B1
• Filed: 11/29/1999
• Issued: 10/09/2001
• Est. Priority Date: 11/27/1998
• Status: Expired due to Fees

• Current Assignee: Kyocera Corporation
• Original Assignee: Kyocera Corporation
• Inventors: Takeda, Shigeki
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Nguyen, Patricia T.
• Application Number:
  US09/449,582
• Time in Patent Office: 680 Days
• Field of Search: 333/202, 333/203, 333/204, 333/206, 333/208, 333/230
• US Class Current: 333/202
• CPC Class Codes: H01P 1/20381 Special shape resonators

Abstract

A distributed element filter is realized which has bandpass characteristics realizing both a flat amplitude characteristic and a flat group delay characteristic throughout the passband at the same time, while realizing transmission zeros in the stopbands. The transfer function s21 of a lowpass prototype filter is expressed by a numerator rational polynomial f(s) having at least one conjugate zeros on the real axis and one conjugate zeros on the imaginary axis and a denominator rational polynomial g(s) as a Hurwitz polynomial of degree 6 or higher; circuit blocks corresponding to the zeros on the real axis and zeros on the imaginary axis are each realized by a multiple resonator filter, and the distributed element filter is realized by a multiple coupling circuit block by setting the conditions on each coupling in corresponding relationship to the zeros on the real axis or zeros on the imaginary axis. The filter having the desired bandpass characteristics can thus be constructed and realized with simple circuitry by using a strict design procedure.

Claims

1. A distributed element filter with bandpass characteristics, constructed of an unbalanced distributed element circuit derived from a transfer function s21 of a lowpass prototype filter, the transfer function s21 being composed of a numerator rational polynomial f(s) and a denominator rational polynomial g(s), wherein the numerator rational polynomial f(s) is an even function of complex frequency s, f(s) has at least conjugate zeros on a real axis and at least conjugate zeros on an imaginary axis, and the denominator rational polynomial g(s) is a Hurwitz polynomial of degree 6 or higher of the complex frequency s, the distributed element circuit comprising:

a multiple coupling circuit block including;

first to fourth resonators;

a first coupling element for connecting the first resonator in cascade with a first external resonator located outward of the first resonator;

a second coupling element for connecting the first resonator and the second resonator in cascade;

a third coupling element for connecting the second resonator and the third resonator in cascade;

a fourth coupling element for connecting the third resonator and the fourth resonator in cascade;

a fifth coupling element for connecting the fourth resonator in cascade with a second external resonator located outward of the fourth resonator;

a sixth coupling element for bridge-coupling a connection point between the first and second coupling elements and the first resonator with a connection point between the fourth and fifth coupling elements and the fourth resonator; and

a seventh coupling element for bridge-coupling a connection point between the first coupling element and the first external resonator with a connection point between the fifth coupling element and the second external resonator,

wherein of the first to seventh coupling elements, the sixth and seventh coupling elements are realized by electric field coupling and, of the first to fifth coupling elements, one or three coupling elements are realized by magnetic coupling and the others by electric field coupling.

2. A distributed element filter with bandpass characteristics, constructed of an unbalanced distributed element circuit derived from a transfer function s21 of a lowpass prototype filter, the transfer function s21 being composed of a numerator rational polynomial f(s) and a denominator rational polynomial g(s), wherein the numerator rational polynomial f(s) is an even function of complex frequency s, f(s) has at least conjugate zeros on a real axis and at least conjugate zeros on an imaginary axis, and the denominator rational polynomial g(s) is a Hurwitz polynomial of degree 6 or higher of the complex frequency s, the distributed element circuit comprising:

a multiple coupling circuit block including;

first to fourth resonators;

a first coupling element for connecting the first resonator in cascade with a first external resonator located outward of the first resonator;

a second coupling element for connecting the first resonator and the second resonator in cascade;

a third coupling element for connecting the second resonator and the third resonator in cascade;

a fourth coupling element for connecting the third resonator and the fourth resonator in cascade;

a fifth coupling element for connecting the fourth resonator in cascade with a second external resonator located outward of the fourth resonator;

a sixth coupling element for bridge-coupling a connection point between the first and second coupling elements and the first resonator with a connection point between the fourth and fifth coupling elements and the fourth resonator; and

a seventh coupling element for bridge-coupling a connection point between the first coupling element and the first external resonator with a connection point between the fifth coupling element and the second external resonator,

wherein the sixth and seventh coupling elements are realized by magnetic field coupling and, of the first to fifth coupling elements, two or four coupling elements are realized by magnetic coupling and the others by electric field coupling.

3. A distributed element filter with bandpass characteristics, constructed of an unbalanced distributed element circuit derived from a transfer function s21 of a lowpass prototype filter, the transfer function s21 being composed of a numerator rational polynomial f(s) and a denominator rational polynomial g(s), wherein the numerator rational polynomial f(s) is an even function of complex frequency s, f(s) has at least conjugate zeros on a real axis and at least conjugate zeros on an imaginary axis, and the denominator rational polynomial g(s) is a Hurwitz polynomial of degree 6 or higher of the complex frequency s,

the distributed element circuit comprising a multiple coupling circuit block including:

first to fourth resonators;

a first coupling element for connecting the first resonator in cascade with a first external resonator located outward of the first resonator;

a second coupling element for connecting the first resonator and the second resonator in cascade;

a third coupling element for connecting the second resonator and the third resonator in cascade;

a fourth coupling element for connecting the third resonator and the fourth resonator in cascade;

a fifth coupling element for connecting the fourth resonator in cascade with a second external resonator located outward of the fourth resonator;

a sixth coupling element for bridge-coupling a connection point between the first and second coupling elements and the first resonator with a connection point between the fourth and fifth coupling elements and the fourth resonator; and

a seventh coupling element for bridge-coupling a connection point between the first coupling element and the first external resonator with a connection point between the fifth coupling element and the second external resonator,

wherein the sixth coupling element is realized by electric field coupling and the seventh coupling element by magnetic field coupling and, of the first to fifth coupling elements, zero or two or four coupling elements are realized by magnetic coupling and the others by electric field coupling.

5. The distributed element filter of any one of claim 3 to 6, wherein the distributed element filter has bandpass characteristics realizing both a flat amplitude characteristic and a flat group delay characteristic throughout a passband thereof at the same time, while realizing transmission zeros in stopbands thereof.

6. The distributed element filter of any one of claim 3 to 6, wherein the multiple resonator filter is composed of distributed element circuit elements formed as a conductive pattern on a dielectric substrate.

7. The distributed element filter of any one of claim 3 to 6, wherein the first and second external resonators are parallel circuits or series circuits having an inductor and a capacitor.

4. A distributed element filter with bandpass characteristics, constructed of an unbalanced distributed element circuit derived from a transfer function s21 of a lowpass prototype filter, the transfer function s21 being composed of a numerator rational polynomial f(s) and a denominator rational polynomial g(s), wherein the numerator rational polynomial f(s) is an even function of complex frequency s, f(s) has at least conjugate zeros on a real axis and at least conjugate zeros on an imaginary axis, and the denominator rational polynomial g(s) is a Hurwitz polynomial of degree 6 or higher of the complex frequency s, the distributed element circuit comprising:

a multiple coupling circuit block including;

first to fourth resonators;

a first coupling element for connecting the first resonator in cascade with a first external resonator located outward of the first resonator;

a second coupling element for connecting the first resonator and the second resonator in cascade;

a third coupling element for connecting the second resonator and the third resonator in cascade;

a fourth coupling element for connecting the third resonator and the fourth resonator in cascade;

a fifth coupling element for connecting the fourth resonator in cascade with a second external resonator located outward of the fourth resonator;

a sixth coupling element for bridge-coupling a connection point between the first and second coupling elements and the first resonator with a connection point between the fourth and fifth coupling elements and the fourth resonator; and

a seventh coupling element for bridge-coupling a connection point between the first coupling element and the first external resonator with a connection point between the fifth coupling element and the second external resonator,

wherein the sixth coupling element is realized by magnetic field coupling and the seventh coupling element by electric field coupling and, of the first to fifth coupling elements, one or three or five coupling elements are realized by magnetic coupling and the others by electric field coupling.