Planar antenna and vehicle window glass

A planar antenna comprising:

• a slot formed in a flat conductor,
• wherein the slot includes
• a first slot extending in a first direction between a first feeding point and a second feeding point,
• a second slot extending in a second direction different from the first direction from an end portion of the first slot in the first direction,
• a third slot extending in a fourth direction opposite to the second direction from an end portion of the first slot in a third direction opposite to the first direction, reaching an open end open in the fourth direction, and
• a J-shaped slot extending in a J-shape from an end portion of the second slot in the second direction to an open end open in the first direction,
• wherein a slot width at an open end of the J-shaped slot is wider than a slot width at the end portion of the second slot in the second direction,
• wherein the J-shaped slot includes a portion that extends in the first direction while maintaining an approximately uniform slot width, and
• wherein the J-shaped slot has an outline resembling half of an ellipse with a long axis approximately parallel to the second direction.