A resonant structure includes a conducting portion extending along a first plane and including first conductors, a ground conductor located away from the conducting portion and extending along the first plane, and a first predetermined number of connecting conductors extending from the ground conductor towards the conducting portion. At least two first conductors are connected to different connecting conductors. A first connecting pair of two of the connecting conductors is aligned along a first direction in the first plane and a second connecting pair of two of the connecting conductors is aligned along a second direction, in the first plane, intersecting the first direction. The resonant structure resonates at a first frequency along a first current path including the ground conductor, conducting portion, and first connecting pair and at a second frequency along a second current path including the ground conductor, conducting portion, and second connecting pair.