An antenna system for a vehicle including a front windshield glass and a rear windshield is disclosed. The antenna system comprises an antenna unit including a radiating element electromagnetically coupled to an excitation element. The radiating element is coupled to the front windshield glass, and the excitation element is positioned on a passenger compartment interior surface of the front windshield glass. The antenna system also comprises a high-gain antenna unit including first radiating elements, a second radiating element, a 90-degree phase shift circuit, and a low noise amplifier that is coupled to the phase shift circuit. The first radiating elements receive signals through the rear windshield glass. The antenna unit and the high-gain antenna unit may function in a diversity antenna configuration.