A plane filter includes a dielectric substrate, a filter part provided on the dielectric substrate, and an input/output line connected to the filter part on the dielectric substrate. The filter part and the input/output line are provided on a front surface of the dielectric substrate. The dielectric substrate includes first and second regions. The filter part is provided in the first region, and the input/output line is provided in the second region. The first region having a first thickness in a first direction toward the front surface from a back surface at a side opposite to the front surface. The second region having a second thickness in the first direction, the second thickness being less than the first thickness. The back surface includes a step corresponding to a difference between the first thickness and the second thickness.
1. A plane filter, comprising:
a dielectric substrate;
a filter part provided on the dielectric substrate; and
an input/output line connected to the filter part on the dielectric substrate,
the dielectric substrate including a front surface and a back surface, the back surface being at a side opposite to the front surface, the filter part and the input/output line being provided on the front surface,
the dielectric substrate further including a first region and a second region, the filter part being provided in the first region, the input/output line being provided in the second region, the second region extending along an outer edge of the dielectric substrate and surrounding the first region,
the first region having a first thickness in a first direction, the first direction being directed from the back surface toward the front surface,
the second region having a second thickness in the first direction, the second thickness being greater than the first thickness, the back surface having a step corresponding to a difference between the first thickness and the second thickness,
a connecting line provided on the first region and linking the input/output line and the filter part,
the input/output line and the filter part being arranged in a second direction along the front surface of the dielectric substrate, the input/output line having a width in a third direction along the front surface of the dielectric substrate, the third direction crossing the second direction,
the connecting line having a width in the third direction, the width of the connecting line in the third direction being less than the width of the input/output line in the third direction.
2. The plane filter according to claim 1 , wherein
the input/output line extends in the second direction; and
the filter part includes a first resonator including first to third lines,
the first line extending in the third direction along the front surface of the dielectric substrate, the first line including a first end and a second end arranged in this order in the third direction,
the second line extending in the third direction, the second line being apart from the first line and facing the first line, the second line including a first end and a second end arranged in this order in the third direction;
the third line extending in the second direction, the third line being connected to the second end of the first line and the second end of the second line.
3. The plane filter according to claim 2 , wherein
the filter part further includes a second resonator including fourth to sixth lines,
the fourth line extending in the third direction, the fourth line including a first end and a second end arranged in this order in the third direction,
the fifth line extending in the third direction, the fifth line being apart from the fourth line and faces the fourth line, the fifth line including a first end and a second end arranged in this order in the third direction,
the sixth line extending in the second direction, the sixth line being connected to the first end of the fourth line and the first end of the fifth line; and
the first resonator and the second resonator are arranged in the second direction and apart from each other, the second line of the first resonator facing the fourth line of the second resonator, the first end of the second line facing the first end of the fourth line, the second end of the second line facing the second end of the fourth line.
4. The plane filter according to claim 3 , wherein
the fourth line and the fifth line have a fourth width and a fifth width respectively in the second direction, and
the fourth width and the fifth width are less than the width in the third direction of the input/output line.
5. The plane filter according to claim 4 , wherein the sixth line has a sixth width in the third direction, and
the sixth width is less than the width in the third direction of the input/output line.
6. The plane filter according to claim 3 , wherein
the first resonator is provided between the input/output line and the second resonator,
the filter part further includes a coupling line extending in the third direction, the coupling line including a first end and a second end arranged in this order in the third direction, and
the coupling line is positioned between the input/output line and the first resonator, the coupling line being apart from the first line of the first resonator and facing the first line of the first resonator, the first end of the coupling line being connected to the input/output line and facing the first end of the first line, the second end of the coupling line facing the second end of the first line.
7. The plane filter according to claim 2 , wherein
the first line and the second line have a first width and a second width respectively in the second direction, and
the first width and the second width are less than the width of the input/output line in the third direction.
8. The plane filter according to claim 7 , wherein
the third line has a third width in the third direction, and
the third width is less than the width in the third direction of the input/output line.