Patent ID: 8130062

Claim:
A microstripline filter comprising: a dielectric substrate; a ground electrode provided on a first surface of the dielectric substrate; a plurality of resonant lines formed on a second surface of the dielectric substrate, the second surface being opposite the first surface, the plurality of resonant lines constituting a plurality of resonators together with the ground electrode and the dielectric substrate; and an input/output electrode coupled to a resonator of the plurality of resonators, wherein the plurality of resonant lines form at least one pair of resonators that are capacitively coupled to each other, wherein at least one of the resonant lines includes (1) an open-end-side electrode having an open end that is parallel to a side edge of a second resonant line in the at least one pair of resonators, the open-end-side electrode having a first line length and a first line width, the first line width being smaller than the first line length; (2) an end-opened electrode that extends from an end on a short-circuit-end side of the open-end-side electrode, the end-opened electrode having a second line length and a second line width, the second line width being smaller than the second line length, the second line width being different from the first line width of the open-end-side electrode, the end-opened electrode being parallel to the side edge of the second resonant line in the at least one pair of resonators, and the end-opened electrode having an open end; and (3) a short-circuit-end-side electrode that extends from the end on the short-circuit-end side of the open-end-side electrode to the ground electrode, the short-circuit-end-side electrode having a third line length and a third line width, the third line width being smaller than the third line length, the third line width being different from the first line width of the open-end-side electrode, a center of the third line width of the short-circuit-end-side electrode being displaced in a direction separating from the end-opened electrode, and wherein the second line width of the end-opened electrode is different from the third line width of the short-circuit-end-side electrode along an entire length of the end-opened electrode, and the third line width of the short-circuit-end-side electrode is smaller than the first line width of the open-end-side electrode.