Patent ID: 6300849
Filing Date: 2001-10-09
Classification: H01P

Abstract:
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; anda 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.