Plane filter

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.