Microstrip line filter

A microstrip line filter, comprising:

• a dielectric substrate;
• a first hairpin resonator disposed on a first layer of the dielectric substrate, wherein the first hairpin resonator comprises a first metal strip, a second metal strip, and a U-shaped metal strip;
• and
• a metal ground layer disposed on a second layer of the dielectric substrate, wherein the metal ground layer comprises a first defected ground structure, the first defected ground structure comprising:
• a first defected area, wherein a projection of the first defected area on the first layer is located inside a hairpin structure of the first hairpin resonator;
• a second defected area, wherein a projection of the second defected area on the first layer is located in a direction opposite to an opening direction of the first hairpin resonator;
• and
• a third defected area connecting the first defected area and the second defected area;
• wherein the U-shaped metal strip comprises a first metal segment, a second metal segment, and a third metal segment, the second segment connects the first metal segment and the third metal segment, and a projection of the third defected area on the first layer is perpendicular to the second metal segment of the U-shaped metal strip, and
• wherein the first defected area is rectangular, the second defected area is rectangular, and the second defected area and the first defected area have the same size.

A microstrip line filter, comprising:

• a dielectric substrate;
• a first hairpin resonator disposed on a first layer of the dielectric substrate, wherein the first hairpin resonator comprises a first metal strip, a second metal strip, and a U-shaped metal strip;
• and
• a metal ground layer disposed on a second layer of the dielectric substrate, wherein the metal ground layer comprises a first defected ground structure, the first defected ground structure comprising:
• a first defected area, wherein a projection of the first defected area on the first layer is located inside a hairpin structure of the first hairpin resonator;
• a second defected area, wherein a projection of the second defected area on the first layer is located in a direction opposite to an opening direction of the first hairpin resonator;
• and
• a third defected area connecting the first defected area and the second defected area;
• wherein the U-shaped metal strip comprises a first metal segment, a second metal segment, and a third metal segment, the second segment connects the first metal segment and the third metal segment, and a projection of the third defected area on the first layer is perpendicular to the second metal segment of the U-shaped metal strip, and
• wherein the first defected area is rectangular, the second defected area is C-shaped, one end of the second defected area is connected to the third defected area, and the third defected area is connected to a corner of the first defected area.