Airborne early warning (AEW) radars provide long-range surveillance from an airborne platform. Their primary targets of interest are hostile aircraft. Long-range radar surveillance coverage can be limited by the range to the horizon; however, satisfactory range can be re-established by placing the surveillance radars at high altitude. The line of sight horizon is then a respectable distance away, the range to the horizon, Rh in kilometers, from a radar at an altitude of h meters is given approximately. The following sections give some example radar parameters for two hypothetical AEW radar systems: one used for fleet protection and the other for long-range airborne surveillance.