A filter includes a dielectric substrate; an electrode layer continuously formed covering a first side of the dielectric substrate; a disk-shaped electrode pattern provided on a second side of the dielectric substrate, the disk-shaped electrode pattern and the electrode layer holding the dielectric substrate therebetween; a ground slot having an opening that is formed asymmetrically with respect to the center of a circular area included in the electrode layer and exposes the dielectric substrate, the circular area and the disk-shaped electrode pattern holding the dielectric substrate therebetween.