A planar antenna manufactured by patterning a substrate consisting of a dielectric layer, and first and second conductive layers applied, respectively, to both opposite surfaces of the dielectric layer. A first slot is formed in the first conductive layer for radiating electric waves. A second slot is formed in the first conductive layer for intercepting a particular frequency of the electric waves radiated by the first slot. A power supply portion is formed with the first conductive layer for supplying electric current to the first slot. A radiating element formed with the second conductive layer, which is excited by the electric waves radiated by the first slot, and radiates the electric waves.