A system designed to provide approach information similar to the ILS (instrument landing system) for aircraft on a final approach to a runway. It provides both lateral and vertical guidance, which is displayed on a conventional course deviation indicator or an approach horizon. The system operates in the C-band microwave frequency range—about 5000 MHz, and the aircraft must be modified to receive these signals besides having special equipment on board. The system's performance is akin to that of an ILS. Its signals can, however, be received only 50° of either side of the inbound course. The ISMLS consists of a C-band (5000 MHz–5030 MHz) localizer, a C-band (5220 MHz–5250 MHz) glide path, a VHF (very high frequency) marker beacon transmitting on 75 MHz, a V/UHF (very/ultrahigh frequency) ILS receiver, a C-band antenna, a converter unit, and a microwave/ILS mode control.