Abstract: A high accuracy broadband antenna system is disclosed. This system is a dual mode system which includes a parabolic reflector dish having a dielectric substrate and a conductive material coating on the substrate; an antenna feed positioned at the focus of the paraboloid and directed at the reflector dish for providing a narrow beam monopulse radiation pattern; and a circuit for coupling energy to and/or from the antenna feed. The conductive material coating on the reflector dish substrate defines a plurality of conductive spiral arms for providing a wide beam monopulse radiation pattern; and the antenna system further includes structure defining a cavity for backing the conductive spiral arms and a circuit for coupling energy to and/or from the conductive spiral arms, whereby the parabolic reflector dish is operable as a primary antenna providing a wide beam radiation pattern.